Why is charity greater than faith (1 Corinthians 13)?

Because faith means you cannot see. God will not let us see him until later, and you can thank Adam and Eve for that, because they saw God face to face, sinned, and were banished, and afterward everyone had to live by faith. Even Abraham, who heard God's voice, was made to struggle, waiting twenty-five years for the promised son and then told to sacrifice him, because God wanted real faith, not a nominal faith, after Adam threw everything away. We have hope for the same reason, because we live in a cursed world that at every turn wants to swallow us up, and you cannot even get out of bed without some degree of hope. But love needs neither faith nor hope: love existed from all eternity in the Trinity, the love of Father, Son, and Holy Spirit, and it will continue for all eternity. You cannot hope for something you already have or believe in something you already see, so faith and hope will pass away when this world is over, but love is eternal, and that is why Paul says the greatest of these is love, because it lasts the longest.