I think the reason why we were able to choose God is merely because He has chosen us in the first place.
However, He gave us that "free will" to respond... :)
"But if serving the LORD seems undesirable to you, then choose for yourselves this day whom you will serve, whether the gods your forefathers served beyond the River, or the gods of the Amorites, in whose land you are living. But as for me and my household, we will serve the LORD" ~Joshua 24:15 (niv)
Still, every choice we can make is only by His grace ^.^