The Psalmist realized that he could not avail himself of all that was typified by the altar, unless, so far as he knew himself, he had washed his hands in innocency. But he also knew that the washing, to be effective, must be in costlier waters than those of his own innocency. The soul requires a Saviour who comes by water and blood, not by water only.
The compassing of the altar is probably a picturesque way of describing the joyous or penitent circle of worshippers that gathered around the altar; and which needed to be prepared for by the usual lustrations, "The baptisms and laying on of hands." We must separate ourselves from known sin, and wash our hands in innocency, if we are to enjoy the blessings of the altar and its sacred associations.
There is the sacrifice of the burnt-offering, which stands for Christ's perfectness and entire devotedness to God on our behalf. But how can we be utterly given up to God unless, so far as we know, we are innocent of presumptuous and cherished sin?
There are the sacrifices of the meal-offering and the peace-offering. But how can we feed on Christ, or feast with Him in holy rapture, whilst we are concealing the stains of the hands that take the food?
There is the sacrifice of the sin offering. But is it .not a sacrilege to claim a share in its blessing if we permit those very sins which cost the Saviour agony and tears? No; we must come out and be separate; we must be willing for God to examine and prove us; we must hate the congregation of the wicked, their conversation and ways; we must occupy ourselves perpetually with the Divine lovingkindness and truth. So only can we compass the altar of God, and taste its comfort and help.