Scripture References:
st. = Num. 6:24-26

The words of “The LORD Bless You and Keep You’ come entirely from Numbers 6:24-26 (RSV), well known as the priestly blessing and the Aaronic benediction. Martin Bucer and John Calvin introduced the Aaronic blessing to Reformed worship after the example set by Martin Luther's Formula Missae ("Formula of the Mass," 1523).

Liturgical Use:
Conclusion of worship, in which case it need not be repeated by the pastor; also appropriate during baptism, ordination, marriage, and other special occasions in Christian worship.

--Psalter Hymnal Handbook