If I have told earthly things and you do not believe, how will you believe if I tell you heavenly things? John 3:12
Jesus is still talking to Nicodemus here, trying to get him to see the big picture. Now, Nicodemus was well-respected, educated, and pious. He was following God as well as he possibly could according to his understanding of God's requirements. HIS understanding. He probably expected to quiz Jesus, examine and cross-examine him, and come away with a 'reasonable' explanation.
"Nicodemus, there are some things you will never understand as long as you rely on your wisdom and experience."
Jesus rocked Nicodemus' faith to its core. He faced a moment of decision. "If I believe what Jesus says about these things … Then I have to change. I have to change my understanding … my attitudes … my actions and behavior. I thought I had God all figured out. What if I don't?"
If you haven't already done so, like Nicodemus, you will come up against a situation that will shake your faith, and you'll come in search of answers. The answers you get will be quite different than what you expect. They will cause you to take a step back, to question what God is doing.
Remember, Jesus says "believe", not "understand". He's not asking us to explain everything, nor is He going to reveal every detail about our situation. He asks us to trust what He does tell us. To trust Him. To believe.