Blessing in the name of God
One of the most significant activities of ministers of the gospel is their opportunity to bless people in the name of Christ. Of course the act of blessing is not restricted to ministers, in that every Christian should bless others. They should bless (rather than curse) even their enemies (Luke 6:28) and they should bless God (James 3:9).
The concept of blessing in the mouth of a minister carries with it special weight. In the Old Testament the priests of Aaron's line had a special blessing for the people (Numbers 6:24-26). Their blessing placed God's name upon the Israelites and conveyed God's blessing to them (Numbers 6:27). Thus in our liturgies the blessing of the minister holds a significant place in the life of the people of God. The presbyter is charged at his ordination with the words: "whose sins you forgive they are forgiven; whose sins you retain they are retained." Of course the minister has no inherent power to forgive sins, any more than he has an inherent power to bless. Rather it is in the office of elder in the church of Christ, a minister of God's word and sacraments, that authorises him to bless in the name of the triune God. The blessing is no trite mantra, nor a merely human device. It is nothing less than the blessing of God almighty, Father, Son and Holy Spirit.
In the Marriage Service, the most significant thing the minister does is to pronounce God's blessing. The vows, after all, are said by the couple to each other. Strictly speaking they marry each other. Marriage can exist without a minister (as it did before the tenth century!). However, the blessing of the minister is a reminder that "those who marry otherwise than God’s word allows are not joined together by God". Thus the minster needs to know if either party is already married to another, for it would be a tragedy were the minster to bless adultery.
I am sometimes asked why minsters raise their hand in blessing. For my own part I raise both hands, with palms upwards rather than downwards - it is a reminder that God is the source of the blessing. This follows the example of our Lord who raised both his hands when he blessed his disciples before departing from their sight (Luke 24:50). There is nothing superstitious or Anglo-catholic about raised hands in blessing, as long as the minister recognises that those whom he blesses are being blessed by God.