The week of prayer for Christian unity has been on my mind a lot in the last few weeks. Recently I was in an extended conversation which touched on the question of what, actually, the unity among Christians is. The Catechism of the Catholic Church speaks of how the Church is "the great sacrament of divine communion" because the Holy Spirit is the "Spirit of communion" and is like the sap of the Father's vine which bears fruit on its branches" (CCC 1108). So, we could say that the unity among Christians is the action and presence of the Holy Spirit who gathers us together.
Seen from one perspective, this unity is not something which anyone can ultimately destroy. But I believe we can be ignorant of or darkened toward God's plan of unity, and therefore we can resist it, we can hinder others from it, we can sin against unity.
How do we foster Christian unity? Dialogue can help, but a program of dialogue is likely to be nothing more than an intellectual exercise, limited in its ability to change lives. If the stuff of Christian unity is the life of the Holy Spirit present in us, then "let us walk in the Spirit" (Gal. 5:25)! Jesus reveals that unity is the desire of His heart in His high priestly prayer before the passion (Jn. 17:20-23). Let us give ourselves fully to the Holy Spirit, to move where he leads. Let us submit ourselves fully to the church, to those who are "over us in the Lord" (1 Thess. 5:12) and to the fullness of that which God has revealed. Let us daily pledge our allegiance to the Father and entrust all that we have and are and do to Him. Let us ask in return the grace to be obedient to His every directive to the fullest possible extent.
In this way, open, listening, watching, following, we will be available to the unity the Lord Himself will build among us.