In His justice He gives the talents in number and kind to those who He predestines.
And in His Mercy ...
By witholding graces from those He foreknows will reject them He's sparing them the punishment that would have come from that rejection.
Does God give sufficient grace to a baby born in the jungles of New Guinea who dies shortly after birth? In a natural sense, that baby never had a chance. But the baby ends up in a state of natural happiness through God's Mercy. So God WOULD give and wills to give everyone sufficient grace to be saved, but sometimes witholds these graces out of His Mercy.