9 “I will worship at Your holy temple, in Your fear.” “At the temple,” we understand as, “near” the temple. For he does not say, I will worship “in” Your holy temple; but, “I will worship at Your holy temple.” It must be understood too to be spoken not of perfection, but of progress toward perfection: so that the words, “I will enter into Your house,” should signify perfection. But that this may come to a happy issue, “I will” first, he says, “worship at Your holy temple.” And perhaps on this account he added, “in Your fear;” which is a great defence to those that are advancing toward salvation. But when any one shall have arrived there, in him comes to pass that which is written, “perfect love casts out fear.” For they do not fear Him who is now their friend, to whom it is said, “henceforth I will not call you servants, but friends,” when they have been brought through to that which was promised.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)