7 There can be no ecumenism worthy of the name without a change of heart. For it is from renewal of the inner life of our minds, from self-denial and an unstinted love that desires of unity take their rise and develop in a mature way. We should therefore pray to the Holy Spirit for the grace to be genuinely self-denying, humble, gentle in the service of others, and to have an attitude of brotherly generosity towards them. St. Paul says: "I, therefore, a prisoner for the Lord, beg you to lead a life worthy of the calling to which you have been called, with all humility and meekness, with patience, forbearing one another in love, eager to maintain the unity of the spirit in the bond of peace". This exhortation is directed especially to those raised to sacred Orders precisely that the work of Christ may be continued. He came among us "not to be served but to serve". The words of St. John hold good about sins against unity: "If we say we have not sinned, we make him a liar, and his word is not in us". So we humbly beg pardon of God and of our separated brethren, just as we forgive them that trespass against us. All the faithful should remember that the more effort they make to live holier lives according to the Gospel, the better will they further Christian unity and put it into practice. For the closer their union with the Father, the Word, and the Spirit, the more deeply and easily will they be able to grow in mutual brotherly love.
Source: Unitatis Redintegratio (Vatican.va)