According to the book of Hebrews, Abraham had true saving faith from the moment he did as God told him to do by leaving Haran to settle in Canaan as a stranger:
“And without faith it is impossible to please Him, for he who comes to God must believe that He is and that He is a rewarder of those who seek Him… By faith Abraham, when he was called, obeyed by going out to a place which he was to receive for an inheritance; and he went out, not knowing where he was going. By faith he lived as an alien in the land of promise, as in a foreign land, dwelling in tents with Isaac and Jacob, fellow heirs of the same promise; for he was looking for the city which has foundations, whose architect and builder is God.” Hebrews 11:6, 8-10 New American Standard Version (NASB)
Abraham’s act of obedience is recorded in Genesis 12:
“Now)the LORD said to Abram, ‘Go forth from your country, And from your relatives And from your father’s house, To the land which I will show you; And I will make you a great nation, And I will bless you, And make your name great; And so you shall be a blessing; And I will bless those who bless you, And the one who curses you I will curse. And in you all the families of the earth will be blessed.’ So Abram went forth as the LORD had spoken to him; and Lot went with him. Now Abram was seventy-five years old when he departed from Haran. Abram took Sarai his wife and Lot his nephew, and all their possessions which they had accumulated, and the persons which they had acquired in Haran, and they set out for the land of Canaan; thus they came to the land of Canaan. Abram passed through the land as far as the site of Shechem, to the oak of Moreh. Now the Canaanite was then in the land. The LORD appeared to Abram and said, ‘To your descendants I will give this land.’ So he built an altar there to the LORD who had appeared to him. Then he proceeded from there to the mountain on the east of Bethel, and pitched his tent, with Bethel on the west and Ai on the east; and there he built an altar to the LORD and called upon the name of the LORD. Abram journeyed on, continuing toward the Negev.” Genesis 12:1-9 NASB
And yet it isn’t until Genesis 15, many years later, that we read of Abraham being credited as righteous before God for trusting in God’s promise to grant him a physical heir:
“After these things the word of the LORD came to Abram in a vision, saying, ‘Do not fear, Abram, I am a shield to you; Your reward shall be very great.’ Abram said, ‘O Lord GOD, what will You give me, since I am childless, and the heir of my house is Eliezer of Damascus?’ And Abram said, ‘Since You have given no offspring to me, one born in my house is my heir.’ Then behold, the word of the LORD came to him, saying, ‘This man will not be your heir; but one who will come forth from your own body, he shall be your heir.’ And He took him outside and said, ‘Now look toward the heavens, and count the stars, if you are able to count them.’ And He said to him, ‘So shall your descendants be.’ Then he believed in the LORD; and He reckoned it to him as righteousness.” Genesis 15:1-6 NASB
This passage is astonishing in its affirmation of the Protestant principle of Sola Fide, e.g., a person is declared righteous and is granted a righteous status before God on the basis of faith in Christ alone, apart from any works of righteousness that an individual performs:
“For we also once were foolish ourselves, disobedient, deceived, enslaved to various lusts and pleasures, spending our life in malice and envy, hateful, hating one another. But when the kindness of God our Savior and His love for mankind appeared, He saved us, not on the basis of deeds which we have done in righteousness, but according to His mercy, by the washing of regeneration and renewing by the Holy Spirit, whom He poured out upon us richly through Jesus Christ our Savior, so that being justified by His grace we would be made heirs according to the hope of eternal life. This is a trustworthy statement; and concerning these things I want you to speak confidently, so that those who have believed God will be careful to engage in good deeds. These things are good and profitable for men.” Titus 3:3-8 NASB
After all, it is Abraham’s faith that God reckons as righteousness even though the patriarch had performed many righteous deeds (along with committing gross sins such as lying about Sarah being his wife). The case of Abraham proves that a person attains a righteous status before God by faith, and that status is maintained throughout one’s whole earthly life, from beginning to end, by faith alone:
“For I am not ashamed of the gospel, because it is the power of God that brings salvation to everyone who believes: first to the Jew, then to the Gentile. For in the gospel the righteousness of God is revealed—a righteousness that is by faith from first to last, just as it is written: ‘The righteous will live by faith.’” Romans 1:16-17 New International Version (NIV)
This is precisely why the blessed Apostle cites the example of Abraham, and specifically quotes Genesis 15:6, to prove his doctrine of Sola Fide:
“What then shall we say that Abraham, our forefather according to the flesh, has found? For if Abraham was justified by works, he has something to boast about, but not before God. For what does the Scripture say? ‘Abraham believed God, and it was credited to him as righteousness.’ Now to the one who works, his wage is not credited as a favor, but as what is due. But to the one who does not work, but believes in Him who justifies the ungodly, his faith is credited as righteousness, just as David also speaks of the blessing on the man to whom God credits righteousness apart from works: ‘Blessed are those whose lawless deeds have been forgiven, And whose sins have been covered. Blessed is the man whose sin the Lord will not take into account.’ Is this blessing then on the circumcised, or on the uncircumcised also? For we say, ‘Faith was credited to Abraham as righteousness.’ How then was it credited? While he was circumcised, or uncircumcised? Not while circumcised, but while uncircumcised; and he received the sign of circumcision, a seal of the righteousness of the faith which he had while uncircumcised, so that he might be the father of all who believe without being circumcised, that righteousness might be credited to them, and the father of circumcision to those who not only are of the circumcision, but who also follow in the steps of the faith of our father Abraham which he had while uncircumcised. For the promise to Abraham or to his descendants that he would be heir of the world was not through the Law, but through the righteousness of faith. For if those who are of the Law are heirs, faith is made void and the promise is nullified; for the Law brings about wrath, but where there is no law, there also is no violation. For this reason it is by faith, in order that it may be in accordance with grace, so that the promise will be guaranteed to all the descendants, not only to those who are of the Law, but also to those who are of the faith of Abraham, who is the father of us all, (as it is written, ‘A father of many nations have I made you’) in the presence of Him whom he believed, even God, who gives life to the dead and calls into being that which does not exist. In hope against hope he believed, so that he might become a father of many nations according to that which had been spoken, ‘So shall your descendants be.’ Without becoming weak in faith he contemplated his own body, now as good as dead since he was about a hundred years old, and the deadness of Sarah’s womb; yet, with respect to the promise of God, he did not waver in unbelief but grew strong in faith, giving glory to God, and being fully assured that what God had promised, He was able also to perform. Therefore it was also credited to him as righteousness. Now not for his sake only was it written that it was credited to him, but for our sake also, to whom it will be credited, as those who believe in Him who raised Jesus our Lord from the dead, He who was delivered over because of our transgressions, and was raised because of our justification.” Romans 4:1-25 NASB
Paul is quite clear. God justifies the ungodly, not because of any works they have done, but because of their faith and trust in Jesus Christ. Paul reasons that the one who seeks to justify himself by his works nullifies grace, since to attain a righteous standing before God on the basis of righteous deeds makes God his debtor. This is why justification is by grace, which God grants because of what Christ has accomplished by his perfect righteousness and obedience, and obedience which including dying on the cross,
“But now apart from the Law the righteousness of God has been manifested, being witnessed by the Law and the Prophets, even the righteousness of God through faith in Jesus Christ for all those who believe; for there is no distinction; for all have sinned and fall short of the glory of God, being justified as a gift by His grace through the redemption which is in Christ Jesus; whom God displayed publicly as a propitiation in His blood through faith. This was to demonstrate His righteousness, because in the forbearance of God He passed over the sins previously committed; for the demonstration, I say, of His righteousness at the present time, so that He would be just and the justifier of the one who has faith in Jesus. Where then is boasting? It is excluded. By what kind of law? Of works? No, but by a law of faith. For we maintain that a man is justified by faith apart from works of the Law. Or is God the God of Jews only? Is He not the God of Gentiles also? Yes, of Gentiles also, since indeed God who will justify the circumcised by faith and the uncircumcised through faith is one.” Romans 3:21-30 NASB
“So then as through one transgression there resulted condemnation to all men, even so through one act of righteousness there resulted justification of life to all men. For as through the one man’s disobedience the many were made sinners, even so through the obedience of the One the many will be made righteous.” Romans 5:18-19 NASB
“In your relationships with one another, have the same mindset as Christ Jesus: Who, being in very nature God, did not consider equality with God something to be used to his own advantage; rather, he made himself nothing by taking the very nature of a servant, being made in human likeness. And being found in appearance as a man, he humbled himself by becoming obedient to death— even death on a cross!” Philippians 2:5-8 NIV
So that it will be based on God’s unmerited favor, since works nullify grace, whereas faith confirms that justification is a free gift of God’s unmerited favor which God grants because of what Christ has wrought:
“and He made no distinction between us and them, cleansing their hearts by faith. Now therefore why do you put God to the test by placing upon the neck of the disciples a yoke which neither our fathers nor we have been able to bear? But we believe that we are saved through the grace of the Lord Jesus, in the same way as they also are.” Acts 15:9-11 NASB
“In the same way then, there has also come to be at the present time a remnant according to God’s gracious choice. But if it is by grace, it is no longer on the basis of works, otherwise grace is no longer grace.” Romans 11:5-6 NASB
The following passage encapsulates the explicit teaching of the God-breathed Scriptures that justification is a declaration and a righteous standing before God that are granted and maintained by faith alone:
“yet we know that a person IS not justified (dikaioutai) by works of the law but through faith in Jesus Christ, so we also have believed in Christ Jesus, in order TO BE justified (dikaioothoomen) by faith in Christ and not by works of the law, because by works of the law no one WILL BE justified (dikaootheesetai).” Galatians 2:16 English Standard Version (ESV)
Here’s another rendering:
“yet we know that no one IS justified by the works of the law but by the faithfulness of Jesus Christ. And we have come to believe in Christ Jesus, so that we MAY BE justified by the faithfulness of Christ and not by the works of the law, because by the works of the law no one WILL BE justified.” New English Translation (NET)
Note the different nuances of the verb dikaioo that the blessed Apostle employs:
Dikaioutai: present indicative middle or passive tense.
Dikaioothoomen: aorist subjunctive passive tense.
Dikaootheesetai: future indicative passive tense.
Paul affirms that a believer has already been justified, is being justified, and shall be justified by faith in Christ. In other words, a person’s past, present and future justification are due solely to faith in Christ apart from works.
Protestant author and apologist William Webster sums up the import of this text:
Some Roman Catholic apologists point out that the verb form for justify is found in the aorist, present and future tenses in the New Testament. They maintain this proves that justification is not a completed work but an ongoing process which is dependent upon the human works of sanctification. However such assertions are laid to rest by Galatians 2:16 where all three verb tenses are found in relation to justification…
Paul states emphatically that no man is ever justified by works, whether it be the past, present or future. He is writing to the Galatians who have already experienced the grace of God. He is warning these believers that justification is not a process based upon human works, even works in cooperation with grace, but solely upon faith in Christ at a point in time. (William Webster, The Biblical Teaching of Justification https://christiantruth.com/articles/articles-roman-catholicism/justification/)
What else do the God-breathed Scriptures need to say to emphasize the fact that justification is a declaration and righteous status maintained by faith from beginning to end?
Dr. James R. White, The God Who Justifies: The Doctrine of Justification (https://www.amazon.com/dp/0764204815?tag=alphandomegmi-20&linkCode=ogi&th=1&psc=1).