DD,
No surprise as this is, I believe, one of the deepest apories of Calvinist theology, where pursuing its own logic to its ultimate consequences leads to system implosion :)
(Divine) grace is free; it just happens; it has no other cause than God's own will which is causeless; it is not required by anything; not explained by any necessity or need -- even ours. We may need it to be "saved" (need relative to a certain end) but from the standpoint of grace we don't need anything -- not even to be saved. The logic of necessity dissolves in the absolute, terrible and wonderful nonsense of grace.
To quote Fernando Pessoa: navegar é preciso, viver nâo é preciso -- freely translated: one may need to sail, one doesn't need to live.
Theologian Eberhard Jüngel has offered an excellent criticism of the concept of necessity in Christian theology in his major work Gott als Geheimnis der Welt (God as Mystery of the World).