Paul said that love is the foundation of everything, and without it, nothing makes sense. No amount of good deeds or going to church on Sundays can justify a lack of love. Why? For he who does not love has not known God, for God is love. This was already written by John. A very simplified and superficial answer, if you want to learn more, read it yourself. This is useful, you don't have to be a believer to read about love in the Bible.
1If I speak with the tongues of men and angels, but have not love, I am a clanging brass or a clanging cymbal.
2If I have the gift of prophecy, and know all mysteries, and have all knowledge and all faith, so that I can move mountains, but do not have love, I am nothing.
3And if I give away all that I have, and give my body to be burned, and have not love, it profiteth me nothing.
4Love is long-suffering, merciful, love does not envy, love is not proud, is not proud,
5he does not commit outrages, does not seek his own, is not provoked, does not think evil,
6He does not rejoice in unrighteousness, but rejoices with the truth;
7He bears all things, believes all things, hopes all things, endures all things.
8 Love never ceases, although prophecies will cease, and tongues will be silenced, and knowledge will cease.
9For we know in part, and prophesy in part; 10But when the perfect thing comes, then that which is in part will cease.
11When I was a child, I spoke like a child, I thought like a child, I reasoned like a child; but when I became a man, I left the things of a child.
12Now we see as if through a dim glass, divinely, but then face to face; now I know in part, and then I will know, even as I am known.
13But now these three remain: faith, hope, and love; but love is the greater of them.
Have you tried reading the New Testament yourself? Or are you just trying to get others interested? I assure you that those who do not believe in God and do not read the Bible are no more interested in Paul's opinions on love than in his own opinions on any other subject.
Paul said that love is the foundation of everything, and without it, nothing makes sense. No amount of good deeds or going to church on Sundays can justify a lack of love. Why? For he who does not love has not known God, for God is love. This was already written by John. A very simplified and superficial answer, if you want to learn more, read it yourself. This is useful, you don't have to be a believer to read about love in the Bible.
1 Corinthians 13: 1-13.
1If I speak with the tongues of men and angels, but have not love, I am a clanging brass or a clanging cymbal.
2If I have the gift of prophecy, and know all mysteries, and have all knowledge and all faith, so that I can move mountains, but do not have love, I am nothing.
3And if I give away all that I have, and give my body to be burned, and have not love, it profiteth me nothing.
4Love is long-suffering, merciful, love does not envy, love is not proud, is not proud,
5he does not commit outrages, does not seek his own, is not provoked, does not think evil,
6He does not rejoice in unrighteousness, but rejoices with the truth;
7He bears all things, believes all things, hopes all things, endures all things.
8 Love never ceases, although prophecies will cease, and tongues will be silenced, and knowledge will cease.
9For we know in part, and prophesy in part; 10But when the perfect thing comes, then that which is in part will cease.
11When I was a child, I spoke like a child, I thought like a child, I reasoned like a child; but when I became a man, I left the things of a child.
12Now we see as if through a dim glass, divinely, but then face to face; now I know in part, and then I will know, even as I am known.
13But now these three remain: faith, hope, and love; but love is the greater of them.
Have you tried reading the New Testament yourself? Or are you just trying to get others interested? I assure you that those who do not believe in God and do not read the Bible are no more interested in Paul's opinions on love than in his own opinions on any other subject.