The following comes from a little very old booklet someone sent me:
We come now to the fruit of the Spirit known as kindliness.
This is a very homely virtue, homely in the British sense of belonging to the home—a very commonplace, ordinary virtue. And yet it is ordinary as salt, and as essential. Without kindliness there is no virtue in the other virtues. It puts a flavor into all the other virtues; without it they are insipid and tasteless; or worse, they degenerate into vices. Love, joy , peace, good temper—without kindliness, they are very doubtful virtues. So it is no chance that this is the middle virtue of the nine, putting flavor into all the others.
So to grow in kindliness is to grow in virtues that are flavored with a certain spirit. The spirit of kindliness pervades everything. The Old Testament, especially the Psalms, uses the expression "loving-kindness." A little boy explained the difference between kindness and loving-kindness: "Kindness is when your mother gives you a piece of bread and butter, but it is loving-kindness when she puts jam on it as well."
But in the New Testament a content has gone into kindness that made adding the "loving" unnecessary. We have quoted a passage into which the content of Jesus has gone into the words: "Treat one another with the same spirit as you experience in Christ Jesus" Not merely the same actions, but the same spirit in the actions as was in Jesus. This is the high water of morality in this universe. Beyond this the human race will not, and cannot, progress. This is character and conduct ultimate. This gives kindness a plus—an infinite plus.
And this saves kindness from mere maudlin sentimentality. It can be very severe—severe because He loves so deeply that He often has to save us by hard refusals. And His kindness can cut—it can cut when, like a surgeon, He insists on cutting out of us moral tumors and cancers. But always His severity is security. It is redemptive. He loves us too much to let us go.