NOTES for Joh 4:43-54
It would appear normal: one can believe only in what has been proven. In reality it is the other way around: exact knowledge is no longer faith. Jesus is speaking precisely about this: you do not want to believe; you want to know. More than that, no matter how much you learn, you will say that it is not enough for you to believe.
In essence, when we set conditions for God, we are simply defending ourselves. Conditions can be set endlessly: "No, now do this too... No, that is not convincing; do this other thing too... No, that is somehow not serious; I think I will consider it some more..." Jesus wants to break this endless chain of proofs. He proposes the reverse order: first there will be faith, and then, not only as an act of God's love but also as a fruit of this faith, healing will take place.
The royal official, asking for a miracle, is not thinking about any kind of proof at all. He is in trouble, he simply needs help, and he comes to Jesus in complete confidence that no one else can help, but He can. In fact, he comes with complete trust. Relying on this trust, on this openness toward God, Jesus says: your son is well. And the royal official, trusting His word, no longer demands that Jesus go in person. If the Lord has said it, then the healing has happened. This kind of trust is precisely the faith that can move mountains.