Protestants (particularly Calvinists) believe that "the infallible rule of interpretation of Scripture is the Scripture itself," meaning that whenever there is a 'dispute' on a given text of Scripture there will necessarily be another verse somewhere in Scripture that speaks more clearly on the matter so as to definitively settle the 'dispute'. An irony here is that while this principle is not taught in Scripture, it is employed throughout the history of Catholic exegesis, while on the flip side it's really the Protestants who are the ones that deny it! This post will prove this beyond a doubt by taking a brief look at how Protestants ignore this principle on one of the most important verses in the Bible, Genesis 15:6.
St Paul quotes Genesis 15:6 in Romans 4:3 to show that Abraham was justified by faith. Protestants take this verse and interpret "faith was reckoned as righteousness" as saying that Abraham's faith was akin to that of an 'empty hand' that had nothing of value to it, but instead it 'reaches out' and takes hold of "Christ's Righteousness". They say that any other interpretation turns faith into a work and thus undermines the Gospel. Not only does the plain reading of the verse suggest no such interpretation, using the principle of Scripture-interprets-Scripture refutes this as well. Most people don't know that Genesis 15:6 is actually quoted three other times in the New Testament, but this is important for exposing the Protestant bias:
Romans 4: 18 In hope he believed against hope, that he should become the father of many nations, as he had been told, “So shall your offspring be.” 19 He did not weaken in faith when he considered his own body, which was as good as dead (since he was about a hundred years old), or when he considered the barrenness of Sarah's womb. 20 No unbelief made him waver concerning the promise of God, but he grew strong in his faith as he gave glory to God, 21 fully convinced that God was able to do what he had promised. 22 That is why his faith was “counted to him as righteousness.”
Galatians 3: 5 He therefore that ministereth to you the Spirit and worketh miracles among you, doeth He it by the works of the law, or by the hearing of faith? 6 Even as Abraham “believed God, and it was accounted to him as righteousness.” 7 Know ye therefore that those who are of faith, the same are the children of Abraham. 8 And the Scripture, foreseeing that God would justify the heathen through faith, preached beforehand the Gospel unto Abraham, saying, “In thee shall all nations be blessed.” 9 So then, those who are of faith are blessed with faithful Abraham.
James 2: 21 Was not Abraham our father justified by works when he offered up his son Isaac on the altar? 22 You see that faith was active along with his works, and faith was completed by his works; 23 and the Scripture was fulfilled that says, “Abraham believed God, and it was counted to him as righteousness”—and he was called a friend of God. 24 You see that a person is justified by works and not by faith alone.
These texts explicitly show the faith Abraham had in Genesis 15:6 was a robust, God-glorifying faith, which God counted as inherently having the quality of righteousness. It was a faith that included hope, grew strong, and was active, rendering Abraham "faithful" in his walk with God. The astonishing thing is, Protestant scholars and apologists routinely ignore these texts when "interpreting" Genesis 15:6. Something's up. Clearly, if Protestants really believed in Sola Scriptura this would not be happening, but in order to salvage Sola Fide they must sacrifice their trust and reliance on the clear teaching of God's Word.