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The Word of God
Sola Scriptura
Everything else on this page rests here. If God has not spoken, we have nothing to say.
God has spoken, and his speech has been written down. The old word for it is inspiration. The Bible did not float down from heaven. Men wrote it, in their own words and settings and styles, and the Holy Spirit carried them along so that what they wrote is what God says.
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, throughly furnished unto all good works.
2 Timothy 3:16-17 (KJV)
Because God breathed it out, and because God does not lie, the Bible is true in all that it affirms. Inerrancy is not a claim that every copy and every translation is perfect. It is a claim about what God gave.
Because God gave it for this purpose, it is enough. Sufficiency means you do not need a new revelation in order to be saved and to live before God. You do not need a private word or a hidden tradition either. The whole counsel of God needed for salvation, faith and life is either expressly set down in Scripture or follows from it by good and necessary consequence, as the Confession says in WCF 1.6.
And because God meant to be understood, the Bible is clear where it matters most. Not every verse is equally easy. Peter said as much about Paul. But the things you must know to be saved are set out clearly enough that an unlearned reader, using the ordinary means, can understand them. WCF 1.7 says so, and it is why a working man with a Bible and a lunch break can feed on the Word of God.
What then about the confessions and catechisms this site holds? They are subordinate standards. They are a faithful summary of what Scripture teaches, tested by the church across centuries, and they sit under the Bible and never beside it.
The supreme Judge, by which all controversies of religion are to be determined, and all decrees of councils, opinions of ancient writers, doctrines of men, and private spirits, are to be examined, and in whose sentence we are to rest, can be no other but the Holy Spirit speaking in the Scripture.
Westminster Confession of Faith 1.10