I grew up thinking UFO's piloted by space aliens were a figment of an overactive imagination. However the U.S. government took UFOs seriously enough that the Air Force had their Blue Book Project to investigate them. I've never seen a UFO myself but I know they are extraterrestrials visiting this planet. I know why they've come and what they're going to do.
God created all things, even the extraterrestrials. Nothing happens outside God's permissive will, including His extraterrestrial creations visiting His earthly creations. Indeed, this is part of God's plan.
God is Almighty enough to have accurately recorded key past events, foretold key future events, and preserved them in the Bible even using His imperfect creation. God did indeed tell of extraterrestrial visits in His Word. But the main reason God gave us His Word was that people would come to know Him through Jesus Christ and have everlasting life. Jesus Christ was God Himself who visited earth as a man (Philippians 2:5-7). He came the first time to die in our place paying the penalty for our sins (Romans 5:8) and be resurrected into an eternal body like what His followers will someday enjoy (1 John 3:2). He is coming back to execute judgment on the earth so that all people will acknowledge His Lordship (Philippians 2:10-11).
Jesus described the conditions in the world when He returns "as the days of Noah were" in Matthew 24:37. He goes on to explain that people will be taken by surprise as they were in the days before the flood carrying on as usual with no expectation of the terrible events about to take place.
There are striking similarities between Noah's day and today. It was a time of violence when men's hearts were hardened against God then (Genesis 6:5, 11) as it is now, but there was also this: "Now it came to pass, when men began to multiply on the face of the earth, and daughters were born to them, that the sons of God saw the daughters of men, that they were beautiful; and they took wives for themselves of all whom they chose.... There were giants on the earth in those days, and also afterward, when the sons of God came in to the daughters of men and they bore children to them. Those were the mighty men who were of old, men of renown" (Genesis 6:1-2, 4).
The only other reference to "sons of God" in the Old Testament is in Job where this term is used for what is clearly fallen angels or demons (Job 1:6, 2:1, 38:7). The Greek myths about the gods may have been based on some truth. The Greek gods were certainly renown mighty men of old.
Fallen angels have the power to appear in different forms. Satan approached Eve as a serpent (Genesis 3:1). The Apostle Paul said, "And no wonder! For Satan himself transforms himself into an angel of light." (2 Corinthians 11:14)
Satan and his minions may have been attempting genetic contamination of humankind as a plot to prevent God's plan to give us the Messiah. But God's plan can not be thwarted. He purged the earth with a flood preserving only Noah and his family because "Noah was a just man, perfect in his generations. Noah walked with God" (Genesis 6:9). Noah was righteous in God's eyes, had a relationship with God, and was also genetically uncontaminated.
Fallen angels mixing it up with humankind on earth is also referenced in the New Testament: "And the angels who did not keep their proper domain, but left their own abode, He has reserved in everlasting chains under darkness for the judgment of the great day" (Jude 1:6)
The fallen angels who were not locked up are now being permitted to visit earth to prepare the world for the lie Satan will use to explain a soon coming supernatural event. Jesus Christ will remove His true followers from the earth all at once in what Christians call "the rapture": "For the Lord Himself will descend from heaven with a shout, with the voice of an archangel, and with the trumpet of God. And the dead in Christ will rise first. Then we who are alive and remain shall be caught up together with them in the clouds to meet the Lord in the air. And thus we shall always be with the Lord" (1 Thessalonians 4:16-17, see also 1 Corinthians 15:51-52).
In his 2nd epistle to the Thessalonians, Paul told them that they would be taken out of the world before the time of God's wrath and that the Antichrist would be revealed after this event (2 Thessalonians 2:3). He also said in verses 9-12, "The coming of the lawless one is according to the working of Satan, with all power, signs, and lying wonders, and with all unrighteous deception among those who perish, because they did not receive the love of the truth, that they might be saved. And for this reason God will send them strong delusion, that they should believe the lie, that they all may be condemned who did not believe the truth but had pleasure in unrighteousness."
How will people in the world rationalize why so many people could instantly vanish from the face of the earth? Most who remain after the rapture will not accept Jesus Christ as God but they will embrace the idea that space aliens zapped or beamed-up millions of people. Unbelievers have been prepared for this lie since 1948 in Roswell, NM, the first major UFO sighting.
There will likely be a visitation of "good" aliens who promise deliverance from the "bad" aliens who threaten the earth and incite the nations to join together in the battle of Armageddon: "I saw three unclean spirits like frogs coming out of the mouth of the dragon, out of the mouth of the beast, and out of the mouth of the false prophet. For they are spirits of demons, performing signs, which go out to the kings of the earth and of the whole world, to gather them to the battle of that great day of God Almighty" (Revelation 16:13-14).
Most who doubt that UFOs even exist hope they really do. They anxiously await the discovery of life elsewhere in the universe to reinforce their theory of evolution and justify a Godless lifestyle (Romans 1:18-22). They dream of the day extraterrestrials will reveal themselves to humankind and weave these visions into science fiction books, movies, and cult doctrines.
Visitations by extraterrestrials are part of the warning to be ready for Christ's return. If you haven't already done so, pray that God will receive you into His Kingdom, acknowledge that you are a sinner in need of salvation and recognize Jesus Christ as Savior. You should do this now while there is yet time. "Believe on the Lord Jesus Christ and you will be saved" (Acts 16:31)!