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Ditto BTNYC.
St. Paul touches on the topic as well as St. John, especially in the Apocalypse. You just about have to keep the extraterrestrial theme in the back of your mind while you read Scripture to see these things. In previous ages we didn't have this problem since alien life was never widely considered as being possible.
You can tell your protestant relatives and friends that the modern myth of so-called evolution and consequently the bad hypothesis that life on other planets is even possible has been the false foundation for alien so-called intelligent life. You can tell them that there are persons of enormous intelligence that are not bound to the earth and did not come from the earth, but normally we refer to them as devils, not human beings. However, nonetheless, they are still persons. Each devil is truly a person, but they are all spiritual beings, without a body. That doesn't prevent them from faking it and appearing to us AS THOUGH they have a body.
Generally prots are willing to pay attention to anyone who takes a stand against 'evolution' because Southern Baptists especially, as well as others, have done much work in developing arguments against so-called evolution.
Tell them as well, if they are willing to listen, that the false gods of so-called evolution are Charles Lyell and Charles Darwin, the demigods Charlie, who based their false system of myth and fables on erroneous interpretation of geological features found on the earth, including but not limited to sedimentary and metamorphic rock strata and fossils.
Ask your prot. friends and relatives if they are Christian. Once they tell you that they are, then ask them if they believe that Jesus Christ is God. Once they tell you they do so believe, then ask them if they also believe that Jesus as God, came to earth as the onlybegotten of the Father (from the Gospel of John), and that He came to redeem all human creatures with his one perfect act of atonement on the Cross (several Scriptures refer to this). When they say they do so believe, then ask them how God could be onlybegotten in Jesus and how there could be only one redemption by which all men would be saved, if there are 'other intelligent beings' not of this world.
If they still don't 'get it' then turn it around. Ask them if we ever meet such 'extraterrestrials' what should we do for them, regarding religion? Should we evangelize to them? Should we offer them Holy Baptism? (You might be wise to question them first on their beliefs on Baptism!)
If they tell you yes (that we should try to make them Christians), then ask them:
What would YOU think if YOU were to travel to a distant planet, to find non-human intelligent life there who would then try to attract YOU to their religion, and invite YOU to undergo their initiation ceremony by which YOU would become a member of their religion? Because that's how the so-called aliens would be looking at us when they come to visit from outer space.
If we would not be interested in joining the religion, foreign to us, of a distant planet, then why should we ever expect any intelligent beings from a distant planet to be interested in joining our religion when it would be foreign to them?
If they say the difference is, that we have the true religion, and they would not, my answer to that is, that we would find that no such alien beings will ever have any interest in being baptized because of one thing, and that is, that devils will never accept Holy Baptism, because they would then have to undergo unimaginable torments that would be inflicted on them by the Sacrament. The pouring of the water on their head would be to them like for us to have molten iron poured on our heads.
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