If I understand correctly, surrender and letting go means not having any longings?
In a way, I think so but it's tricky to discuss because of the duality of language. So let me use specific examples rather than talk theoretically and generally.
Suppose you believe it is very important in life to treat other people with decency, say that you have been taught and believe that God loves us equally. This is not too hard to imagine if you believe in God and especially a loving God. In this what you become a person who is morally oriented to doing good by other people and want to argue that point as a virtue to, say believe in getting anything they can get by any means available, who could care less who they hurt to get that. How to you prove there is a loving God. How do you make an argument that is irrefutable, that can't be denied? I believe that if you are honest you can't, not even to yourself and so the result becomes that love and hate are equal, there is no good or evil, all things are permissible, as you mentioned with Dostoevsky. And the result is tremendous existential suffering. Everything ones soul yearned for is empty of meaning. The wind blows where it blows and doesn't care about anything.
This is being driven off a cliff by a tiger to see another below. No exit, no escape, no hope. So all of this is because we are fixated, we need proof of our ideals, we want to bring the force of reason into the equation and all is futility. All our longing but empty dreams, tears shed in the rain. There is only the dark abyss. So you let go and fall in. You surrender and die to will. When all ones efforts to hold on collapse and that intense focus is released, the mind can open to other things, one of which is that to love is all that matters. It is by being that God whatever expresses. The kingdom of heaven isn't in a logical proof somewhere, it is with us. There is nowhere to go, nothing to do, nothing to become, nothing to prove. Those who are, know.