As a Calvinist and a believer in predestination, many people have asked me, “Why do you evangelize?” The logic being that since God is sovereign in salvation, and has predestined all who will come to him, that there is no need to evangelize since no matter what you do, the job will still get done. That, of course, is wrong thinking.
Calvinism holds these three three things true simultaneously: God is sovereign, man is responsible, and Christians are to witness and pray.
Consider what God says to the Israelites before they go into battle for the Promised Land: “The Lord has given your enemies into your hand.” Now, the Israelites didn’t just sit around after that and say, “Why fight the battle? God has already won it for us!” That’s because God doesn’t make things happen in spite of what we do. That’s fatalism. He makes things happen because of what we do.
For an expanded discussion of these truths, check the excellent Parchment & Pen blog here.