I think we are then getting into the realm of, "Why were the Elect elected?" Under the doctrine of Original Sin, which teaches that no one can come to God apart from the grace of God, there really isn't a lot of options out there to explain the how election takes place. The dominant view among early reformers was sovereign election, where election takes place by predestination (based on God's wisdom and will).  Within the Protestant circle, the competing view of sovereign election is prevenient grace taught by Arminianism (which is a borrowed idea from the RCC). In this view, the grace of God is at work in every one equally, overcoming the power of the Original Sin, and election happens by foreknowledge (of man's response and faith). While I like the idea of prevenient grace, there is no Bible passage on which I can firmly base that doctrine.

While admitting that the Will of God may never be fully known, the Bible does seem to provide some answers. For me, what convinced me personally that believers are elected by predestination is based in Romans 9: "Not only that, but Rebekah’s children were conceived at the same time by our father Isaac. Yet, before the twins were born or had done anything good or bad — in order that God’s purpose in election might stand: not by works but by him who calls — she was told, 'The older will serve the younger.' Just as it is written: 'Jacob I loved, but Esau I hated.'"

I think the natural reading would have been: God did not base his election on Isaac and Esau's conduct, but based on Isaac and Esau's faith. The problem with this explanation is that God still based his decision on Isaac and Esau's quality, which seems to go against the flow of the text, where God's decision "does not, therefore, depend on human desire or effort, but on God’s mercy." I do see faith within the realm of human desire and effort.

Elsewhere, a view of "decision based in foreknowledge" also seem to undermine the sense of God's majesty and sovereignty. For example, when Jesus speaks of "All those the Father gives me will come to me, and whoever comes to me I will never drive away.", the tone would be awkward if "all those" would have had faith and come to Christ regardless of whether the Father had given them to him or not.

The "election by predestination" in no way invalidates the importance of human choice. Rather, it attempts to explain the reason of that choice. So instead of one considering all pros & cons and making a decision to commit himself to Christ, "election by predestination" suggest an invisible hand which guide that person to faith. 

Philosophically speaking (beware, now I'm getting into logic), I don't believe that any man is "free" apart from his background, personality, previous experince, and so on. I believe that any choice we make is no more than the culmination of our past enabling us to consider what is good or not good for us. So God, in his infinite wisdom, guide and mold those whom he has chosen, so they would know what truly is good or not good for them in eternity.