Albert Barnes Commentary Galatians 5:14

"For the whole law is fulfilled in one word, [even] in this: Thou shalt love thy neighbor as thyself." — Galatians 5:14 (ASV)

For all the law is fulfilled. That is, this expresses the substance of the whole law; it embraces and comprises all. The apostle, of course, here alludes to the law in regard to our duty to our fellow-men, since that was the point which he particularly enforces. He is saying that this law would counteract all the evil workings of the flesh; and, if this were fulfilled, all our duty to others would be discharged. A similar sentiment he has expressed in Romans 13:8-10.

The turn here in the discussion is worthy of particular notice. With great skill he changes the subject from a doctrinal argument to a strain of practical remark, and furnishes most important lessons for the right mode of overcoming our corrupt and sensual passions, and discharging our duty to others.

Thou shalt love thy neighbour (Matthew 19:19).