helplesspilgrim, ConstantineTG,
That the ministers of the Holy Mystery of Matrimony were the couple is the original belief, in the east, and later the shepherd of the Church was added.
The form of marriage approved by the Church is needed for the validity of marriage, so it not only the couples valid consent that makes the marriage valid. **In either west or east the clergy provide the blessing, and the couple are the ministers. ** The law is that the blessing must normally be obtained from the bishop or priest for validity, or permitted by a deacon for the Latin Church. (Normally, because you can see there is an exception where is it not possible, for a month, even although valid, in the eastern churches the blessing is to be obtained as soon a possible). A deacon in the eastern churches cannot give any blessings (but a Latin deacon can), only priests or bishops.
CCC 1623 According to the Latin tradition, the spouses as ministers of Christ’s grace mutually confer upon each other the sacrament of Matrimony by expressing their consent before the Church. In the traditions of the Eastern Churches, the priests (bishops or presbyters) are witnesses to the mutual consent given by the spouses,[Cf. CCEO, can. 817] but for the validity of the sacrament their blessing is also necessary.[Cf. CCEO, can. 828]
CCEO
Canon 817
- Matrimonial consent is an act of the will by which a man and woman, through an irrevocable covenant, mutually give and accept each other in order to establish marriage.
- No human power can replace this matrimonial consent.
Canon 832
- If one cannot have present or have access to a priest who is competent according to the norm of law without grave inconvenience, those intending to celebrate a true marriage can validly and licitly celebrate it before witnesses alone:
(1) in danger of death;
(2) outside the danger of death, as long as it is prudently foreseen that such circumstances will continue for a month.
- In either case, if another priest, even a non-Catholic one, is able to be present, inasmuch as it is possible he is to be called so that he can bless the marriage, without prejudice for the validity of a marriage in the presence only of the witnesses.
- If a marriage was celebrated in the presence only of witnesses, the spouses shall not neglect to receive the blessing of the marriage from a priest as soon as possible.
CIC
Canon 1057
- A marriage is brought into being by the lawfully manifested consent of persons who are legally capable. This consent cannot be supplied by any human power.
- Matrimonial consent is an act of will by which a man and a woman by an irrevocable covenant mutually give and accept one another for the purpose of establishing a marriage.
Canon 1116
- If one who, in accordance with the law, is competent to assist, cannot be present or be approached without grave inconvenience, those who intend to enter a true marriage can validly and lawfully contract in the presence of witnesses only:
(1) in danger of death;
(2) apart from danger of death, provided it is prudently foreseen that this state of affairs will continue for a month.
- In either case, if another priest or deacon is at hand who can be present, he must be called upon and, together with the witnesses, be present at the celebration of the marriage, without prejudice to the validity of the marriage in the presence of only the witnesses.
Theological Basis
vatican.va/roman_curia/congregations/cfaith/cti_documents/rc_cti_1977_sacramento-matrimonio_en.html
CEEO
intratext.com/IXT/ENG1199/_PMP.HTM#5
CIC
intratext.com/IXT/ENG0017/_P3Z.HTM