In the day of his true restoration, therefore, God once more really dwells in man. We do not say, however, that he actually enters and takes full possession at once. Just as soon as man gives his exiled Father permission to enter as a whole God and a God forever, he enters effectually; but ordinarily he enters by degrees, and in accordance with the usual laws and operations of the human mind. He does not break the vessel of man's spirit, nor mar its proportions, nor deface anything which is truly essential to it; but gradually enters into all parts of it, readjusts it, removes the stains which sin had made upon it, and fills it with divine light. Man's business in this great work is a very simple one. It is to cease all resistance, and to invite the Divine Master of the mind to enter it in his own time and way. And even this last is hardly necessary. God does not wait even to be invited to come, except so far as an invitation is implied in the removal of the obstacles which had previously kept him out. Man's ceasing from all resistance, and his willingness to receive God as the all in all, and for all coming time, may be regarded as essentially the completion of the work in respect to himself; but the work of God, who is continually developing from the soul new powers and new beauties, can be completed only with the completion of eternity.
edited from A Treatise on Divine Union (1851) Part 7, Chapter 2 by Thomas Cogswell Upham. You can find his website, managed by Craig L Adams, here: http://thomascupham.blogspot.com