Every believer is to be a teacher.
Knowledge without obedience does not advance a person. The Hebrews had long enough been exposed to the gospel to be teaching it to others, but were babies, too infantile and unskilled to comprehend, let alone teach, the truth of God.
Commentary from the MacArthur study Bible, notes for Hebrews 5:12,13.
In verses 14:15-31 of John, Jesus promises believers comfort from 5 supernatural blessings that the world does not enjoy: 1) a supernatural Helper (vv. 15-17); 2) a supernatural life (vv. 18,19); 3) a supernatural union (vv. 20-25); 4) a supernatural Teacher (v. 26); and 5) a supernatural peace (vv. 27-31). The key to all of this is John 14:15 which relates that these supernatural promises are for those who love Jesus Christ, whose love is evidenced by obedience.
Commentary from the MacArthur study Bible, summary notes for John 14:15-31.