58 From the reaffirmation of an already existing communion of faith, the Second Vatican Council drew pastoral consequences which are useful for the everyday life of the faithful and for the promotion of the spirit of unity. By reason of the very close sacramental bonds between the Catholic Church and the Orthodox Churches, the Decree on Eastern Catholic Churches Orientalium Ecclesiarum has stated: "Pastoral experience clearly shows that with respect to our Eastern brethren there should and can be taken into consideration various circumstances affecting individuals, wherein the unity of the Church is not jeopardized nor are intolerable risks involved, but in which salvation itself and the spiritual profit of souls are urgently at issue. Hence, in view of special circumstances of time, place and personage, the Catholic Church has often adopted and now adopts a milder policy, offering to all the means of salvation and an example of charity among Christians through participation in the Sacraments and in other sacred functions and objects". In the light of experience gained in the years following the Council, this theological and pastoral orientation has been incorporated into the two Codes of Canon Law. It has been explicitly treated from the pastoral standpoint in the Directory for the Application of Principles and Norms on Ecumenism . In so important and sensitive a matter, it is necessary for Pastors to instruct the faithful with care, making them clearly aware of the specific reasons both for this sharing in liturgical worship and for the various regulations which govern it. There must never be a loss of appreciation for the ecclesiological implication of sharing in the sacraments, especially in the Holy Eucharist.
Source: Ut Unum Sint (Vatican.va)