EXOD198 Now since man is obviously confined within time and space, his deeds cannot penetrate beyond a certain limit -- the furthest point his merit can reach. Hence Scripture has advised us that when we see the merits of our forefathers becoming exhausted, we should ourselves awaken the attributes of God's goodness and chesed for us, by clinging in our deeds to the same virtues. Then, measure for measure, His chesed will envelop us and will never depart from us. (The expression lo yamush carries the implication of "will never depart", as in [this verse], lo yamish -- "the pillar of cloud shall not at any time depart.")