I hold that it squares perfectly. That someone is to be passed over is only known to God. We humans cannot possibly know who is to be saved and who is not. From our perspective, scripture teaches us to go out into the fields and evangelize as if all were the elect. This is God's will and we are to obey.
Certainly our witnessing is not useless, it just does not achieve the actual salvation. God does that. It is part of God's perfect plan that we Christians go out and spread the Good News. That's what Jesus did.
The beauty of this view is that we have a burden lifted from us. Have you ever witnessed to a person and nothing happened? Did you ever feel guilty, like maybe if you had said something differently or better that maybe a soul could have been won for Christ? I have, but no more. Now I know that my job isn't to win souls, it is to spread the Word. God saves the souls. In this context, I am an instrument for His use, nothing more.