Why is it so easy for people to believe that Jesus Christ will return and “rapture” those who love Him, leaving behind the rest of the world, but those same people find it impossible to believe that Jesus Christ came for His mother and assumed her, body and soul, into heaven?
Some Christians will believe in the Rapture, but not the Assumption of Mary. Both are about human bodies being taken up into Heaven. I think people forget the the Assumption of Mary is not the Ascension of Mary. Even Elijah was taken up into Heaven! The Church does not teach that Mary went up by her own power; rather, her son took her to be with him. It is by Jesus' power that the Blessed Mother is assumed into Heaven.
The Assumption of Mary also anticipates the bodily resurrection of the faithful. St. Paul teaches that:
At the resurrection of the dead, we shall be changed: raised with an imperishable, immortal body. Mary has already been given that grace.
51 Listen, I will tell you a mystery! We will not all die, but we will all be changed, 52 in a moment, in the twinkling of an eye, at the last trumpet. For the trumpet will sound, and the dead will be raised imperishable, and we will be changed. 53 For this perishable body must put on imperishability, and this mortal body must put on immortality. 1Corinthians 15:51-53
The Catholic Church teaches that:
966 "Finally the Immaculate Virgin, preserved free from all stain of original sin, when the course of her earthly life was finished, was taken up body and soul into heavenly glory, and exalted by the Lord as Queen over all things, so that she might be the more fully conformed to her Son, the Lord of lords and conqueror of sin and death." The Assumption of the Blessed Virgin is a singular participation in her Son's Resurrection and an anticipation of the resurrection of other Christians.--Catechism of the Catholic ChurchNow there's a lot of theology in that paragraph. Today, let's keep it simple. The Assumption of Mary is about a son taking his mother home to be with him. It's act of love from Jesus to Mary.
It's about family being together.