It is not merciful to look through time and choose an elect based on their good works. That is cause and effect. Scripture is full of references to the mercy of God. The ideas do not mix. Mercy indicates a salvation from a wrath deserved. To say God chose based on your prospective work denies the originality of God's election decision. Rewarding is not original - it is based on the recipient's deserving action. But mercy is original. There is no deserving action. Just the opposite of deserving action. God rewarded Christ by having mercy on the elect.