Mark with what insatiable earnestness he invokes these blessings upon them, that they may not be tossed about. But how shall this be effected? By the "Holy Spirit in your inward man, that Christ may dwell in your hearts through faith." How again shall this be?
Thus when, writing to the Ephesians, he spoke of "Christ dwelling in their inner man," he meant, no doubt, that the Lord ought to be admitted into their senses. He then added, "in your hearts by faith, rooted and grounded in love,"-making "faith" and "love" not substantial parts, but only conceptions of the soul.
Paul prays that believers be made more steadfast, not doubting but believing increasingly that Christ dwells in them even when they do not see him with their physical eyes. He prays that the Spirit which has been given them might infuse into them a certainty that Christ lives and is the Son of God, so that he lives by faith in their hearts. Thus when we have faith in him we behold him in our hearts. The benefit of this is that we grow more sure of his blessing. He does not desert us. He is always present through that faith in him which he guards in us. The gift of the Spirit, which is also the gift of God the Father, is given to us that he may keep us safe, to his glory.
[AD 407] John Chrysostom on Ephesians 3:16-17