In the mystery of the Assumption is expressed the faith of the Church

By the mystery of the Assumption into heaven there were definitively accomplished in Mary all the effects of the one mediation of Christ the Redeemer of the world and Risen Lord: "In Christ shall all be made alive. But each in his own order: Christ the first fruits, then at his coming those who belong to Christ" (1 Cor. 15:22-23). In the mystery of the Assumption is expressed the faith of the Church, according to which Mary is "united by a close and indissoluble bond" to Christ, for, if as Virgin and Mother she was singularly united with him in his first coming, so through her continued collaboration with him she will also be united with him in expectation of the second.

"Redeemed in an especially sublime manner by reason of the merits of her Son,"(109) she also has that specifically maternal role of mediatrix of mercy at his final coming, when all those who belong to Christ "shall be made alive," when "the last enemy to be destroyed is death" (1 Cor. 15:26)." …

Thus in her Assumption into heaven, Mary is as it were clothed by the whole reality of the Communion of Saints, and her very union with the Son in glory is wholly oriented towards the definitive fullness of the Kingdom, when "God will be all in all."

Saint John Paul II, Encyclical letter Redemptoris Mater, March 25, 1987, n. 41