She who at the Annunciation called herself the "handmaid of the Lord" remained throughout her earthly life faithful to what this name expresses. In this she confirmed that she was a true "disciple" of Christ, who strongly emphasized that his mission was one of service: the Son of Man came not to be served but to serve, and to give his life as a ransom for many" (Mt. 20:28). In this way Mary became the first of those who, "serving Christ also in others, with humility and patience lead their brothers and sisters to that King whom to serve is to reign,"113 and she fully obtained that "state of royal freedom" proper to Christ's disciples: to serve means to reign!
"Christ obeyed even at the cost of death, and was therefore raised up by the Father (cf. Phil. 2:8-9). Thus he entered into the glory of his kingdom. To him all things are made subject until he subjects himself and all created things to the Father, that God may be all in all (cf. 1 Cor. 15:27-28)."
Mary, the handmaid of the Lord, has a share in this Kingdom of the Son.
The glory of serving does not cease to be her royal exaltation: assumed into heaven, she does not cease her saving service, which expresses her maternal mediation "until the eternal fulfillment of all the elect."116 Thus, she who here on earth "loyally preserved in her union with her Son unto the Cross," continues to remain united with him, while now "all things are subjected to him, until he subjects to the Father himself and all things." 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."
In this phase too Mary's maternal mediation does not cease to be subordinate to him who is the one Mediator, until the final realization of "the fullness of time," that is to say until "all things are united in Christ" (cf. Eph. 1:10).
John Paul II, Redemptoris Mater § 41