Ecumenism is a movement that has arisen in the Church which seeks the
union of all Christian Churches.  All those who believe in Christ and
are baptized have the right to be called Christians and are obliged
to fulfill Jesus' great wish that all people be united in one flock.
There are many difficulties in the way of the union of all Christians,
because there exist different criteria for the interpretation of
Sacred Scripture, the discipline, and the orientation of the Church.
But all true Christians are somewhat united with Christ in faith and
love.  We can understand then that outside the Catholic Church are
found extremely valuable elements, and that even the sacred rites of
other Churches lead to communion with the Lord.  The Spirit of Christ
does not refrain from making use of them as a means of salvation.
The ecumenical movement must be undertaken by all Christians. First,
we should get to know one another, in a special manner through
contacts on the level of equality.  When doctrinal matters are
discussed at such meetings, it should always be with the consent of
the bishop.

We Catholics must realize that there is an order or hierarchy in the
truths of faith, and that not all of them have the same relationship
with the fundamentals of the faith.  The sphere in which our
collaboration with other Christians can take place with more efficacy
is the collaboration in the social sphere.  We should strive to
increase amity and collaboration without a spirit of polemics, and we
must realize that the lives of many of our brothers and sisters show
with great evidence the admirable fruit of their faith and love in
Jesus Christ.

REFERENCE: New Saint Joseph SUNDAY MISSAL AND HYMNAL Complete Edition
In Accordance with Vatican II, Catholic Book Publishing Co.