Understanding the Word of God adds knowledge; doing it removes foolishness.
Removing temptation by cutting out your eye may seem excessive; but removing the situation that creates temptation in the first place is an act of prudence.
It is a decision of the head, and that is loving God by doing the first commandment.
Biblical meaning of full, perfect or complete:
Made whole or complete by adding or subtracting.
Matthew 18:8 Wherefore if thy hand or thy foot offend thee, cut them off, and cast them from thee: it is better for thee to enter into life halt or maimed, rather than having two hands or two feet to be cast into everlasting fire.
Matthew 18:9 And if thine eye offend thee, pluck it out, and cast it from thee: it is better for thee to enter into life with one eye, rather than having two eyes to be cast into hell fire.
Mark 12:30 And thou shalt love the Lord thy God with all thy heart, and with all thy soul, and with all thy mind, and with all thy strength: this is the first commandment.