John Chrysostom, on Ps 126:1

“Unless the Lord build the house, they labour in vain that build it. Unless the Lord keep the city, he watcheth in vain that keepeth it.”

“"That good thing that was committed to you to keep"—how?—"by the Holy Spirit, who dwells in us." For it is not in the power of a human soul, when instructed with things so great, to be sufficient for keeping them [of himself]. And why? Because there are many robbers and thick darkness, and the devil is still at hand to plot against us; and we know not what is the hour, what the occasion for him to set on us. How then, he means, shall we be sufficient for keeping them? "By the Holy Spirit"—that is if we have the Spirit with us, if we do not expel grace, he will stand by us. For, "Except the Lord build the house, they labor in vain who build it. Except the Lord keep the city, the watchman wakes but in vain." This is our wall, this our castle, this our refuge. If therefore he dwells in us and is himself our guard, what need is there for the commandment? That we may hold him fast, may keep him and not banish him by our evil deeds.”

Imported from an open dataset — not yet checked against the printed edition.