18 Let no one cheat you of your reward, taking delight in false humility and worship of angels, intruding into those things which he has not seen, vainly puffed up by his fleshly mind,
19 and not holding fast to the Head, from whom all the body, nourished and knit together by joints and ligaments, grows with the increase that is from God.
cheat (v.18) = a compound word in Greek meaning “to give judgment against” and “to act as an umpire” — let no man decide for or against you.
your reward (v.18) — Let no one decide what you should do or what you should worship. They will deprive you of your rewards at the Judgment Seat.
worshiping (v.18) = outward show of religion
worshiping of angels (v.18) — as the Gnostics did.
The worship of angels involved a show of humility, an affectation of superior reverence for God, as shown in the reluctance to attempt to approach God otherwise than indirectly; in its assumption that humanity, debased by the contact with matter, must reach after God through successive graces of intermediate beings. — Wuest, page 211.
not (v.18) — probably not in the original — so it should read “those things which he has seen” — visions (easily faked, unverifiable)
fleshly (v.18) — of the sin nature — the carnal mind
Not connecting to the head (Christ) results in obstruction of the channel of spiritual life which prevents growth (v.19).
Each believer is thought of as forming a vital connection with Christ the Head. Thus joined to Him, they all become the joints and ligaments by which the whole body (the church) is supplied with energy and life. The heretical teacher, without this contact with Christ, cannot possibly contribute to the growth of the church. — Vaughan, page 84.