Love is the greatest thing
Though I speak with the tongues of men and of angels, and have not charity, I am become as sounding brass, or a tinkling cymbal. And though I have the gift of prophesy, and understand all mysteries and all knowledge; and though I have all faith, so that I could remove mountains, and have not charity, I am nothing. And though I bestow all my goods to feed the poor, and though I give my body to be burned, and have not charity, it profiteth me nothing. 1 Cor. 13:1-3
Charity is agape, or love. The apostle Paul had just spent a whole chapter talking about the necessity and the usefulness of the diversity of spiritual gifts in the church, but he ended by saying, "and yet I shew unto you a more excellent way" (1 Cor. 12:31). What is this "more excellent way"? It is the way of love. In other words, all the spiritual gifts together are less excellent than the one spiritual fruit of love.
In fact, as the apostle says at the beginning of chapter 13, you could have all the spiritual gifts and be the most dedicated and zealous Christian on the planet and yet be nothing. Nothing! I take that to mean that all the profit and advantage that one's spiritual giftedness gives them in the end amounts to nothing if they are not a genuinely loving person.
The reason for the absolute necessity of love is not hard to see. Love is the "bond of perfectness" (KJV) that "binds everything together in perfect harmony" (Col. 3:14, ESV). It is the reason the apostle will tell the Corinthians at the end of the letter, "Let all your things be done in charity" (1 Cor. 16:14). Without love, it would be impossible for the church to function as it ought. Take away love, and it's like taking the oxygen out of the room: there is just no way for genuine and living and robust spiritual vitality to exist in that environment. Love is the glue that holds the church together.
Love is also the greatest witness for the reality of our religion. Church, do you want to reach the world? Imitate Christ and be loving people: "By this shall all men know that ye are my disciples, if ye have love one to another" (Jn. 13:35). That does not mean that we don't stand for truth. But let us not be like the Ephesian church which our Lord rebuked because it knew how to hate false doctrine but it didn't know how to love (Rev. 2:4, 6). We grow through truth, yes, but only as we speak the truth in love (Eph. 4:15).
And note that love is not just a feeling. Of course you want the feeling to be there, but that is not how Paul describes love in verses 4-7. Love is selflessness. It is being kind and patient, putting away boasting and pride and irritability. It means putting others first. It means dying to yourself!
How do we do that? We do it, not out of the resources of our own flesh, but through the resources of the Spirit of God. Those who are born again love God and love those who are begotten by him (1 Jn. 5:1-2). We do because of the love of Christ which constrains us (2 Cor. 5:14). So let us live lives of love in the power of the Spirit and motivated by the grace of our Lord Jesus Christ. May it be said of us, as it was of the early church, "Behold how they love one another!" There is no better apologetic for our faith.