God's Word indicates that the early Church had access to a body of authoritative instruction, and that there was even an established way of teaching doctrine.
Romans 6:17 – [Paul gives thanks, saying,] "But God be thanked, that ye were the servants of sin, but ye have obeyed from the heart that form of doctrine which was delivered you."
2 Timothy 1:13 – "Hold fast the form of sound words [teaching], which thou hast heard of me, in faith and love which is in Christ Jesus."
Acts 2:42 – "And they continued steadfastly in the apostles' doctrine."
2 Thessalonians 2:15 – "Therefore, brethren, stand fast, and hold the traditions which ye have been taught, whether by word, or our epistle."
Acts 20:27 – "For I have not shunned to declare unto you all the counsel of God."