Apostle From Space (1978)
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Spaceman lands off coast of Florida and seeks refuge in a church, where he is taken in by the local minister. Meanwhile, having been alerted to the arrival by radar, the government begins searching for the mysterious visitor, hypothesizing that he might actually be a Cuban spy. Back at the church, the minister names the spaceman "Peter" and begins teaching him English. The minister is especially excited because he has seen "Peter" the spaceman kneel before the cross in church and pray, thereby suggesting an intergalactic validity to Christianity.
At the big United Nations speech, "Peter" tells us his planet is smaller, more advanced, etc. They only noticed us when we made a trip to the moon, and have sent "Peter" to find out if our intentions for space travel are hostile or peaceful. We appear peaceful...for now--they'll keep watching. "Peter" then "dissolves" as he walks down a corridor, apparently transported back to his home world. He takes a Bible with him as a souvenir.