Bonhoeffer was a Lutheran Theologian executed by the Nazis.

Nothing can make up for the absence of someone whom we love, and it would be wrong to seek a substitute; we must simply hold out and see it through. That sounds very hard at first, but at the same time, it is a great consolation, for the gap, as long as it remains unfilled, preserves the bonds between us. It is nonsense to say that God fills the gap; God doesn’t fill it, but on the contrary, keeps it empty and so helps us to keep alive our former communion with each other, even at the cost of pain.