John 14:17 the Spirit of truth, whom the world cannot receive, because it neither sees Him nor knows Him; but you know Him, for He dwells with you and will be in you.
John 15:26 But when the Helper comes, whom I shall send to you from the Father, the Spirit of truth who proceeds from the Father, He will testify of Me.
It’s the scripture which was intended to “make us wise unto salvation”. Do you think God wouldn’t make it possible to follow His only inspired word with the “testimony” of the Holy Spirit?
2 Timothy 3:15 And that from a child thou hast known the holy scriptures, which are able to make thee wise unto salvation through faith which is in Christ Jesus. 16 All scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness: 17 That the man of God may be perfect, thoroughly furnished unto all good works.
The gospel is “made manifest” or made known to all nations “by the scriptures of the prophets”. Not by interpretations of men.
Romans 16:26 But now is made manifest, and by the scriptures of the prophets, according to the commandment of the everlasting God, made known to all nations for the obedience of faith:
Read this. He promised the Holy Spirit, but I dispute that 2 Timothy 3:15 teaches Sola Scriptura.
http://www.ewtn.com/library/scriptur/solascri.txt
As I am fond of pointing out, the Bible is inerrant, but your reading is fallible.