“Then the Pharisees and Sadducees came, and testing Him asked that He would show them a sign from heaven. He answered and said to them, "When it is evening you say, 'It will be fair weather, for the sky is red'; and in the morning, 'It will be foul weather today, for the sky is red and threatening.' Hypocrites! You know how to discern the face of the sky, but you cannot discern the signs of the times. A wicked and adulterous generation seeks after a sign, and no sign shall be given to it except the sign of the prophet Jonah." And He left them and departed.” (Matthew 16:1-4, NKJ)Jesus effectively told the sign seekers that if the miracle of His resurrection did not convince them, nothing would. Unfortunately miracles do not convert people as Abraham told the certain rich man who wanted Lazarus to warn his brothers about eternal consequences: “If they do not hear Moses and the prophets, neither will they be persuaded though one rise from the dead” (Luke 16:31).
In order to discern the signs if the times, it is necessary to know God’s Word and believe it. The only way to believe God’s Word is to know Him. Only those who know God through Jesus Christ have a correct understanding of who He is (John 14:6). And this is necessary to appreciate that God is Almighty enough to declare “the end from the beginning” in His Word (Isaiah 46:10).
As even religious people missed recognizing Jesus as the Messiah because of their inability to discern the times when He was here the first time; so too will there be people who think they are Christians left behind at the Rapture. I’d expect the Rapture to shake many of them up enough that they would become believers but there will be a convincing enough explanation that most will embrace (2 Thessalonians 2:11).
We live in "perilous times" (2 Timothy 3:1). Don’t think you can skate by having only a superficial relationship with Jesus. There are great deceptions coming… “For false christs and false prophets will rise and show great signs and wonders to deceive, if possible, even the elect” (Matthew 24:24). The only way to prepare for such times is to have a good working understanding of God’s Word. It is an exciting time to be alive for those truly alive through Jesus Christ.