When missionaries are tempted to think that they have something to do with people getting saved, we need to be reminded that salvation is “all of God”. The following quote from Spurgeon–a commentary on Psalm 3:8, brings home that point:

Search Scripture through, and you must if you read it with a candid mind, be persuaded that the doctrine of salvation by grace alone is the great doctrine of the word of God: “Salvation belongeth unto the Lord.” This is a point concerning which we are daily fighting. Our opponents say “Salvation belongeth to the free will of man; if not to man’s merit, yet at least to man’s will;” but we hold and teach that salvation from first to last, in every iota of it, belongs to the Most HIght God. It is God that choses his people. He calls them by his grace; he quickens them by his Spirit, and keeps them by his power. It is not of man, neither by man; “not of him that willeth, nor of him that runneth, but of God that showeth mercy.” May we all learn this truth experimentally, for our proud flesh and blood will never permit us to learn it in any other way.

For more on the Sovereignty of God from the Psalms, check out Divine Satisfaction.