Adam Clarke on Psalms 134:2

Lift up your hands in the sanctuary - קדש kodesh, "in holiness:" or, as the Syriac, lekoudishe, "to holiness;" in sancta, Vulgate; and εις τα ἁγια, Septuagint; "in holy things; or, as the Aethiopic, in the house of the sanctuary." The expression seems very similar to that of St. Paul, 1Tim 2:8 : "Lifting up holy hands, without wrath and doubting."

Bless the Lord - That is, speak good of his name: tell the wonders he has wrought, and show that his name is exalted.