I am glad that I do not have to worry that I am not holy enough and therefore might be "left behind" when Jesus returns. Jesus reigns now in the church and the one time when He returns He will judge the living and the dead, make all things new, take me to Himself. He is my righteousness, not any moral acts I do. Even the believing is a gift, nothing that I contribute.
And because of him [God] you are in Christ Jesus, who became to us wisdom from God, righteousness and sanctification and redemption, so that, as it is written, “Let the one who boasts, boast in the Lord.” 1Corinthians 1:30-31
Whoever believes and is baptized will be saved, but whoever does not believe will be condemned. Mark 16:16
The "Left Behind" theology, aka "Dispensational Pre-millenialism", is a relatively new way of looking at end times. It began in the 1800's, and it robs Jesus Christ of His central place as the Redeemer of fallen man, and instead shifts the emphasis to man being ready enough to be raptured away before the tribulation, as well as looking to current events and the re-establishment of the temple in Jerusalem as a means to predict Christ's coming. Lutherans historically have held to the "a-millennial" position, that Christ is now reigning in His church, and will come back once for judgement, then make all things new, as I mentioned above.
Amen. Come, Lord Jesus! Revelation 22:20