Farming in the world needs the cooperation of the four essential elements. A harvest is gathered into the barn only as the result of the natural action of water, earth, wind, and light. God's farming likewise has four elements - faith, hope, love, and knowledge. Faith is our earth. It is that in which we take root. Hope is the water which nourishes us. Love is the wind through which we grow. Knowledge is the light by which we ripen.
Gospel of Philip 79:18-30 (A late second-century Valentinian gospel)
Commentary: This Valentinian analogy is an exegesis of 1 Corinthians 13. Compare 1 Corinthians 13:13 - "So faith, hope, and love abide, these three: but the greatest of these is love." Why four instead of three? Because a careful reader of 1 Corinthians 13 will notice that Paul talks about knowledge, but about how our knowledge is imperfect and passes away. This suggests that there is a knowledge that is perfect and abides, and it is this knowledge which the Valentinians are claiming here. It is the knowledge that Paul speaks about in 13:2 as his ability to understand "all mysteries and all knowledge." But this is nothing alone, he says, just as "faith" in the absense of love is nothing. So this Valentinian teacher is saying that knowledge is not enough on its own, but must operate along with faith, hope and love. The four together are essential to spirituality.