68 Our union in and with Christ is first evident from the fact that, since Christ wills His Christian community to be a Body which is a perfect Society, its members must be united because they all work together towards a single end. The nobler the end towards which they strive, and the more divine the motive which actuates this collaboration, the higher, no doubt, will be the union. Now the end in question is supremely exalted; the continual sanctifying of the members of the Body for the glory of God and of the Lamb that was slain. The motive is altogether divine: not only the good pleasure of the Eternal Father, and the most earnest wish of our Savior, but the interior inspiration and impulse of the Holy Spirit in our minds and hearts. For if not even the smallest act conducive to salvation can be performed except in the Holy Spirit, how can countless multitudes of every people and every race work together harmoniously for the supreme glory of the Triune God, except in the power of Him, who proceeds from the Father and the Son in one eternal act of love?
Source: Mystici Corporis Christi (Vatican.va)