Jesus' love stands in complete contrast and contradiction to every bit of earthly Human love. The new testament writers had a bad problem. In order to describe the great, wonderful, divine, warm love of God they had come to know, they had to choose from four Greek words, because the New Testament was written in Greek. They had four Greek words to choose from. So that's the word they chose.
Agape love is just the opposite to human love.
You love your wife because she loves you back, or you love your children because they are your children. There's always a reason We love only when we are loved back. But God's love is unconditional. It just flows from Him without cause, totally independent of our goodness or our works. He is and what He is.