Albert Barnes Commentary Luke 6:40

"The disciple is not above his teacher: but every one when he is perfected shall be as his teacher." — Luke 6:40 (ASV)

The disciple is not, etc. The learner is not above his teacher, does not know more, and must expect to be treated no better. This seems to have been spoken to show them that they were not to expect that their disciples would go beyond them in attainments; that if they were blind, their followers would be also; and that therefore it was important for them to understand fully the doctrines of the gospel, and not to be blind leaders of the blind.

Every one that is perfect. The word translated is perfect (or, alternatively, shall be perfected as his master) sometimes means to repair or mend, and is used this way for mending nets (Matthew 4:21; Mark 1:19). Therefore, it means to repair or amend in a moral sense, or to make whole or complete. In this context, it evidently means thoroughly instructed or informed. The Christian should be like his master—holy, harmless, and undefiled, and separate from sinners. He should copy his example, and grow into the likeness of his Redeemer. Nor can any other be a Christian.