This passage is referring to the fact that if a husband and wife want to have a child they can have a child. But we can't come close to God just because we want to or someone else wants us to. You can't even be saved by God's desires. God desires for everyone to be saved. But not everyone will be saved.
Salvation is like receiving a gift.
We're pretty experienced at that. It is a gift, nothing that you have ever done can earn you closeness to God. Jesus Christ died on the cross to take away our sins or we could never come close to God. Salvation is like going through a door. Shepherds in those days when they wanted to bed their sheep down for the night would herd their sheep into an enclosure made of stones or branches and then the shepherd would lay down across the opening and the shepherd would literally be the door.