What does Galatians 5:15 mean?

Paul has shown that for Christians to try to live under the law of Moses is a waste of their freedom in Christ (Galatians 3:23–29; 5:1–6). Now he is showing that serving only ourselves is also a waste of that freedom. Instead, we must use that freedom to serve each other in self-sacrificing love (Galatians 5:7–14). This love motive will become the replacement for all of the law of Moses.

Why is this so essential for those in Christ? For one thing, any group made up of people who serve only themselves will eventually fall into conflict. Others will—inescapably—get in the way of our agenda, and the ability to perfectly meet our own desires. To always have things "our way," we will either have to turn aside from the needs of others, or charge on through, trampling on those needs directly. Inevitably, those collisions will lead to the destruction of the entire group.

As James put it, a life lived according to the worldly wisdom of serving self doesn't lead to human happiness. Instead, it leads to "disorder and every vile practice" (James 3:16), along with coveting, quarreling, and fighting (James 4:1–3). As Paul puts it here, we end up devouring and consuming each other in order to try to get what we want.

The alternative is to use our Christ-won freedom to set ourselves aside and serve each other in love. Not only does that lead to greater joy for all of us, it is living as Jesus would as we live free in Him.