This encyclical from 1995 is both a great recap of the efforts of the Catholic Church in fostering ecumenism since the Second Vatican Council and a deep meditation on the importance and necessity of working for the reintegration of Christian denominations so that we may all be one in God as Jesus prays in John 17. The two keys are (1) to desire unity with the pureness of heart found in genuine Love and (2) to seek the truth about others and ourselves and God and the bible. No small order, but that is what we are called to. The encyclical is very inspiring and is intended not only for church leaders at the highest levels but for all Christians, for we are all called to unity in Christ.
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