Many believers have already died without being raptured and they are rewarded according to their righteous deeds done while on earth. Some are His Bride and some are not. (read the parable of The Banquet and how we are not just to assume the highest position) The Rapture is an event which takes place at the end of the Church Age. Prior to this event Jesus evaluates and judges His churches (people). They are warned of the consequences of their failures if no changes are made (no repentance) or exhorted by future rewards for faithfulness and obedience. (Please read revelation chapters 2 and 3) Before the Second Coming Jesus comes for His Bride (The Rapture). Not all in the churches qualify as His Bride as noted in Revelation 2,3. Some are unfaithful, unrepentant and "unworthy" of Him - Jesus. So... They are "ashamed at His coming" because they are not "ready to meet Him." They are spotted and wrinkled, not without blame in the world - they are not properly "dressed" for the wedding. They will be left out (not raptured) but also, not necessarily lost either. But they will now be purified and tested by the fires of Great Tribualtion so that .... the next time they meet Jesus either as a matyr or otherwise - they will hopefully, be "made ready"

“Let us rejoice and be glad and give the glory to Him, for the marriage of the Lamb has come and His bride has MADE HERSELF READY.” It was given to her (the privilege) to clothe herself in fine linen, bright and clean; for the fine linen is...... the righteous acts of the saints. (Revelation 19:7,8)

Consider this -
The Bride is taken out from the Body of Christ.... just as Eve was taken out from the body of Adam to be his wife. Jesus is referred to as the second Adam. God did not take Adam's whole body and present it to Him as His wife only a small portion which was very close to his heart.

Please read (1 John 2:24-29)
So... YOU MUST REMAIN FAITHFUL to what you have been taught FROM THE BEGINNING. IF you do, you will remain in fellowship with the Son and with the Father. 25And in this fellowship we enjoy the eternal life he promised us.
26I am writing these things TO WARN YOU about those who want to lead you astray. 27But you have received the Holy Spirit, and he lives within you, so you don’t need anyone to teach you what is true. For the Spirit teaches you everything you need to know, and what he teaches is true—it is not a lie. So.... just as HE HAS TAUGHT YOU, REMAIN IN FELLOWSHIP with CHRIST JESUS.
28And now, dear children, REMAIN in fellowship with Christ SO THAT when he returns, (for you - however) you will be full of courage and not shrink back from him in shame.
29Since we know that Christ is righteous, we also know that all who do what is right are God’s children. (1 John 2:24-29)

You hopefully, would not accept a betrothed who was unfaithful, an adulterer , disobedient and unrepentant - who showed up on your wedding day dressed in filthy rags - expecting to be married to you ? Is God not JUST to give each of us according to our deeds? Will He now give His precious, perfect Son to just anyone who is not "WORTHY of HIM?"

“If you love your father or mother more than you love me, you are "NOT WORTHY OF BEING MINE;" or if you love your son or daughter more than me, you are "NOT WORTHY OF BEING MINE." 38If you refuse to take up your cross and follow me, you are "NOT WORTHY OF BEING MINE." - Jesus (Matthew 10:37,38)