We ought carefully to examine whether the doctrine offered us is conformable to Scripture, and if not, to reject it. Nothing must be added to the inspired words of God; all that is outside Scripture is not of faith, but is sin.Prolegomena, 2, Work 3, Ascetic (iii).
The Word comes first, and with the Word the Spirit breathes upon my heart so that I believe.Luther's Works, Vol. 54 : Table Talk (Augsburg Fortress, 1999, [c] 1967)
By the nature of the highest genera and of first principles; for those things are known by themselves and are not susceptible (anapodeikta) of proof which cannot be demonstrated by any other, otherwise the thing would go on to infinity. Hence Basil says 'it is necessary that the first principles of every science should be self-evident' (anankē hekastēs mathēseōs anexetastous einai tas archas, In Psalmum cxv homilia, PG 30.104–5). Thus Scripture, which is the first principle in the supernatural order, is known by itself and has no need of arguments derived from without to prove and make itself known to us.
O, grant, that being ruled by thy Spirit, we may surrender ourselves to thee, and so acquiesce in thy Word alone, that we may not deviate either to the right hand or to the left, but allow thee alone to be wise, and that acknowledging our folly and vanity, we may suffer ourselves to be taught by thy Word.Lecture 36 on Jeremiah
Since the entirety of Holy Scripture is the word of the Lord, no testimony could possibly be better, more certain, or more efficacious. For if God, who cannot lie, has spoken something in his own Scripture, which is itself a mirror of his will, then it is true.On the Truth of Holy Scripture, 1.15