I recognize that this verse is in the context of Jesus teaching a particular lesson, namely service. Jesus is washing the feet of his disciples, and when he gets to Peter, Peter does not quite understand.
(John 13:7) Jesus answered him, “What I am doing you do not understand now, but afterward you will understand.”
I think there is another timeless principle to be extracted as well. How often are we situations, or have choices to make, and various other things, and wonder, “God, what are you doing?”
And sometimes I think His response is that we should trust Him: “What I am doing you do not understand now, but afterward you will understand.”
How often it is that afterward, we are able to perceive, or at least think we perceive, the reasons things happened, for going through a period of testing and trial, or out of love for God and love for others did something we did not particularly desire to do, but after seeking understanding from the Lord, or reflection, it makes a lot more sense to us.
God reminds us, “For my thoughts are not your thoughts, neither are your ways my ways, declares the Lord. For as the heavens are higher than the earth, so are my ways higher than your ways and my thoughts than your thoughts.” (Isaiah 55:8-9)