21 "This change of heart and holiness of life, along with public and private prayer for the unity of Christians , should be regarded as the soul of the whole ecumenical movement, and can rightly be called 'spiritual ecumenism' ". We proceed along the road leading to the conversion of hearts guided by love which is directed to God and, at the same time, to all our brothers and sisters, including those not in full communion with us. Love gives rise to the desire for unity, even in those who have never been aware of the need for it. Love builds communion between individuals and between Communities. If we love one another, we strive to deepen our communion and make it perfect. Love is given to God as the perfect source of communion—the unity of Father, Son and Holy Spirit—that we may draw from that source the strength to build communion between individuals and Communities, or to re-establish it between Christians still divided. Love is the great undercurrent which gives life and adds vigour to the movement towards unity. This love finds its most complete expression in common prayer . When brothers and sisters who are not in perfect communion with one another come together to pray, the Second Vatican Council defines their prayer as the soul of the whole ecumenical movement . This prayer is "a very effective means of petitioning for the grace of unity", "a genuine expression of the ties which even now bind Catholics to their separated brethren ". Even when prayer is not specifically offered for Christian unity, but for other intentions such as peace, it actually becomes an expression and confirmation of unity. The common prayer of Christians is an invitation to Christ himself to visit the community of those who call upon him: "Where two or three are gathered in my name, there am I in the midst of them" ( Mt 18:20).
Source: Ut Unum Sint (Vatican.va)