In regard to this focused determination on God and scripture, Reformed Theology is built around 5 core principles:
Sola Gratia (Grace Alone):
Salvation is the wholly unmerited gift from God to man. It is a product of faith alone, it cannot be gained through works alone.
Ephesians 2:4-5: But God, being rich in mercy, because of the great love with which he loved us, even when we were dead in our trespasses, made us alive together with Christ, by grace you have been saved.
Ephesians 2:8-9: “For by grace are ye saved through faith; and that not of yourselves: it is the gift of God: Not of works, lest any man should boast.”
1 Peter 1:3–5: Blessed be the God and Father of our Lord Jesus Christ! According to his great mercy, he has caused us to be born again to a living hope through the resurrection of Jesus Christ from the dead, to an inheritance that is imperishable, undefiled, and unfading, kept in heaven for you, who by God’s power are being guarded through faith for a salvation ready to be revealed in the last time.
2 Corinthians 12:9-10: And He said to me, “My grace is sufficient for you, for My strength is made perfect in weakness.” Therefore most gladly I will rather boast in my infirmities, that the power of Christ may rest upon me. Therefore I take pleasure in infirmities, in reproaches, in needs, in persecutions, in distresses, for Christ’s sake. For when I am weak, then I am strong.
Sola Fide (Faith Alone):
Christians are justified, ie. their salvation is verified, by faith alone. This is not to say that works are not vital (James certainly had something to say about that), but works are a manifestation of faith, they are not the dominant means for salvation or justification. Even works mandated by the Law itself were not enough to merit a salvation that was not already given by God through Jesus’ sacrifice.
Galatians 3:11: “But that no man is justified by the law in the sight of God, it is evident: for the just shall live by faith.”
Philippians 3:8-9: For his sake I have suffered the loss of all things and count them as rubbish, in order that I may gain Christ 9 and be found in him, not having a righteousness of my own that comes from the law, but that which comes through faith in Christ, the righteousness from God that depends on faith.
Romans 4 1-3; 9-10: “What then shall we say that Abraham, our forefather, discovered in this matter? If, in fact, Abraham was justified by works, he had something to boast about—but not before God”. What does the Scripture say? “Abraham believed God, and it was credited to him as righteousness.” “Is this blessedness only for the circumcised, or also for the uncircumcised? We have been saying that Abraham’s faith was credited to him as righteousness. Under what circumstances was it credited? Was it after he was circumcised, or before? It was not after, but before!”
Galatians 3:10-14: For all who rely on works of the law are under a curse; for it is written, “Cursed be everyone who does not abide by all things written in the Book of the Law, and do them.” Now it is evident that no one is justified before God by the law, for “The righteous shall live by faith.” But the law is not of faith, rather “The one who does them shall live by them.” Christ redeemed us from the curse of the law by becoming a curse for us—for it is written, “Cursed is everyone who is hanged on a tree”— so that in Christ Jesus the blessing of Abraham might come to the Gentiles, so that we might receive the promised Spirit through faith.
Galatians 2:19: For through the law I died to the law so that I might live to God. I have been crucified with Christ, and I no longer live, but Christ lives in me. The life I live in the body, I live by faith in the Son of God, who loved me and gave Himself up for me. I do not set aside the grace of God. For if righteousness comes through the law, Christ died for nothing.
Solus Christus (Christ Alone):
Jesus Christ is the only way to salvation and the sole mediator between man and God. No other authority is it necessary for one to be saved. Jesus is also the High Priest to His people. So, if someone needs something ordained or conferred by a priest, Jesus is already there. Just as the might and grace of God was not contained or limited to Mosaic Law in the Old Testament, the salvation brought to man through Jesus is not constrained by laws and orders in the New Testament. Just as God is sufficient in all things, so is Jesus.
1 Timothy 2:5: “For there is one God, and one mediator between God and men, the man Christ Jesus.”
John 14:6: Jesus answered, “I am the way and the truth and the life. No one comes to the Father except through me.
Acts 4:11-12: This Jesus is the stone that was rejected by you, the builders, which has become the cornerstone. And there is salvation in no one else, for there is no other name under heaven given among men by which we must be saved.”
Hebrews 4:14-16: Since then we have a great high priest who has passed through the heavens, Jesus, the Son of God, let us hold fast our confession. For we do not have a high priest who is unable to sympathize with our weaknesses, but one who in every respect has been tempted as we are, yet without sin. Let us then with confidence draw near to the throne of grace, that we may receive mercy and find grace to help in time of need.
Matthew 4:10: Then Jesus said to him, “Be gone, Satan! For it is written, “‘You shall worship the Lord your God and him only shall you serve.”
Revelation 15:4: Who will not fear, O Lord, and glorify your name? For you alone are holy. All nations will come and worship you, for your righteous acts have been revealed.”
1 Colossians 3:17: And whatever you do, in word or deed, do everything in the name of the Lord Jesus, giving thanks to God the Father through him.
Sola Scriptura (Scripture Alone)
Scripture alone is the only infallible source of divine revelation and the final authority for matters of faith and practice. Sola Scriptura does not mean that all truth is contained in the Bible, but rather that all mankind needs to know pertaining to salvation and doing what is pleasing to God is contained within its pages. A secondary assertion of equal importance, is that scriptures cannot be superseded in manners of doctrinal truth.
This is why Reformed Christians do not view traditions as extensions to the Word and thus additions from tradition are not necessary for salvation. The most powerful argument for this is the High Priestly Prayer spoken by Jesus in John 17 (1-26), where He states that He accomplished God’s work by teaching people the Word and seeing that they kept it. He follows this with the important distinction that He had preached the Truth and people had received it, so that scripture would be fulfilled. All of this He set up before He returned to God, effectively closing the book on any argument for additional practices being necessary for salvation. Apart from that, here are other verses attesting to the sufficiency of the scripture alone:
2 Timothy 3:16-17: “All Scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness: That the man of God may be perfect, thoroughly furnished unto all good works.”
Psalm 19:7: The law of the Lord is perfect, reviving the soul; the testimony of the Lord is sure, making wise the simple.
1 John 5:13. “These things have I written unto you that believe on the name of the Son of God: that ye may know that ye have eternal life and that ye may believe on the name of the Son of God.”
Acts 20: 26-27: Therefor, I testify to you this day that I am innocent of the blood of all, for I did not shrink from declaring to you the whole counsel of God.
The Apostles, particularly John and Luke, did not talk much of successors or the divine powers instated in church offices, but they spoke at length about false doctrines coming from those who followed after them.
Acts 20:28-30: Pay careful attention to yourselves and to all the flock, in which the Holy Spirit has made you overseers, to care for the church of God, which he obtained with his own blood. I know that after my departure fierce wolves will come in among you, not sparing the flock; and from among your own selves will arise men speaking twisted things, to draw away the disciples after them.
John 2: 18-20: Children, it is the last hour, and as you have heard that antichrist is coming, so now many antichrists have come. Therefore we know that it is the last hour. They went out from us, but they were not of us; for if they had been of us, they would have continued with us. But they went out, that it might become plain that they all are not of us. But you have been anointed by the Holy One, and you all have knowledge.
Soli Deo Gloria (Glory to God Alone):
God’s glory is the highest good and therefore is the purpose for which we were created. We were made to glorify Him, to reflect His glory, and to proclaim it to all creation. Salvation must be sola fide, sola gratia, and solus Christus — through faith alone, by grace alone, and on account of Christ alone —
Attributing redemption to our efforts, or those of another authority in any way is to rob God of His full glory. If God and God alone is not the one who saves, then He shares His glory with creatures. But as the prophet Isaiah tells us, God will share His glory with no one.
Isaiah 42:8: “I am the Lord; that is my name! I will not yield my glory to another or my praise to idols.
1 Peter 4:11: Whoever speaks, is to do so as one who is speaking the utterances of God; whoever serves is to do so as one who is serving by the strength which God supplies; so that in all things God may be glorified through Jesus Christ, to whom belongs the glory and dominion forever and ever. Amen.
1 Corinthians 6:19-20: Or do you not know that your body is the temple of the Holy Spirit who is in you, whom you have from God, and you are not your own? For you were bought at a price; therefore, glorify God in your body and in your spirit, which are God’s.
Revelation 15:4 Who will not fear You, O Lord, and glorify Your name? For You alone are holy. All nations will come and worship before You, for Your righteous acts have been revealed. “
Each of these tenets will be described exegetically at length in following chapters. For now, this simply serves as an introduction and framework for future arguments. The purpose of this framework is to establish grounds for the guidance of the Holy Spirit and the consistency of God’s actions and rationale in scripture.
The Bible may have been physically written by over 30 different men, but they profess a single divine author. Not just inspired, but in part authored, God was always direct with His chosen. If the Bible is the word of God, it must be inerrant and its tone unchanging. Anyone can take a verse out of context and mold it to fit their narrative, but taken in context of the whole book, there can only be one true narrative of the Bible.