To me God predestined according to what he foreknew. In other words he predestined those He knew would trust in him, for eternal life.
That's an Arminian approach, but it's not one I agree with. Scripture speaks of God predestining us, of God choosing us, and not us choosing God.
For Lutherans predestination isn't about God picking and choosing who will and won't be saved, but instead to bring us the comfort to know that God has chosen us in Christ, and the Gospel promise we have received is true and faithful. I am God's child, I belong to God, because I am a baptized Christian--I can know I am God's not by anything I find in myself, but instead of the external reality of God's word, as it is preached and also given through the Sacraments. I belong to God, how can I know this? Because the Gospel which I hear say so, because the Baptism which I received makes me Christ's, in the Lord's Supper I receive the body and blood of Jesus broken and shed for me. This Word comes to me, assures me of God's grace and promises, and by which I can in confidence say I belong to Jesus Christ because
He says so.
It isn't about God simply knowing in advance, God actually has chosen us, and we can know this because of the promise we have from God in Jesus by the Gospel.
What this doesn't mean, is that God has rejected anyone, or that anyone is predestined to damnation; for we read clearly in Scripture that God desires that all be saved, that He is the Savior of all men. Christ died for everyone, because God loves everyone, and the Gospel is for everyone. God withholds His mercy from none, nobody is outside the scope of God's grace and salvation in Jesus Christ. From a Lutheran perspective, this is where Calvinism goes wrong. By saying that Christ only died for the elect, rather than for the whole world; by saying that God picks and chooses who will and won't be saved, rather than that it is the will of God that all be saved. It is true that God has predestined us in Christ to salvation, that we did not choose Him but that He chose us, apart from anything meritorious in ourselves (not even our own "yes"); but it is not true that God ignores or rejects anyone, the Gospel is clear, Christ died for the ungodly, the unworthy, the sinners--for everyone, and Christ and this Gospel is for everyone.
-CryptoLutheran