The scriptures, and the illumination of the Holy Spirit!
the HS leads the apostles into all truth and they teach us. Acts 8 Jn 16:13
We must be taught by Peter, the apostles, and their successors! Matt 28:19 Jn 21:17
Matt 28:19 Go ye therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost:
Lk 1:4 That thou mightest know the certainty of those things, wherein thou hast been instructed.
Acts 8:30 And Philip ran thither to him, and heard him read the prophet Esaias, and said, Understandest thou what thou readest?
31 And he said, How can I, except some man should guide me? And he desired Philip that he would come up and sit with him.
Jesus Christ continues HIS ministry in His new covenant church thru Peter, the apostles, and their successors with the same mission, power, and authority!
Mt 16:18 Mt 28:19 Acts 1:17 acts 8:31 & 35 Lk 10:16 Jn 8:32 Jn 13:20 Jn 16:13
Jn 20:21-22 eph 2:20