John Gill Commentary Psalms 134:2

"Lift up your hands to the sanctuary, And bless ye Jehovah." — Psalms 134:2 (ASV)

Lift up your hands [in] the sanctuary
Which Aben Ezra interprets of the priests lifting up their hands to bless the people; but Kimchi, better, of lifting up of the hands to God in prayer; see (Psalms 141:2) ; which should be done "with holiness", as the Targum renders it, in a holy manner; and is the same with lifting up holy hands, (1 Timothy 2:8) ; or towards the holy place; the oracle in the holy of holies, and the ark of the covenant, typical of Christ; see (1 Kings 8:29 1 Kings 8:30) (Psalms 28:2) ; so Kimchi; or rather, according to Arama, unto the holy name of God, to whom prayer is to be directed;

and bless the Lord ;
which is repeated, to show the importance of the work, that it might not be forgotten and neglected; this being a principal part of spiritual service, and greatly acceptable to God.