We're in the middle of a mission at the moment (prayers always welcome!). One of the things we're doing is door-knocking our neighbourhood and we've seen people turn to the Lord even on the door-step. Praise God!
In our morning meetings there seems to be one kind of prayer that recurs more than any others - that God would prepare hearts so that when we arrive they are open to the gospel. Now I'll give a hearty Amen to all such prayers and, in His grace, God may well grant this. But when we think about hearts opened, wouldn't it be better to pray that the word itself will open hearts, conquer unbelief, awaken faith? Is it possible that we're separating word and Spirit by conceiving of evangelism in these terms? Is there a danger that the power is thought of as separate from the gospel and not as the gospel itself? (Rom 1:16).
I think I'd rather pray, "Lord, though the people we meet be stone-hearted, blind and lost in sin and blackest darkness, bring life and immortality to light through your gospel. May your word do its almighty work and bring life from the dead."
I'd certainly rather conceive of evangelism in those terms. When we tell the gospel we're not basically hoping that some have previously enjoyed God's power. Rather, we're going with the power of God which is unleashed upon all, every time we speak of Christ.