“We may always come boldly to God’s throne, assuring ourselves that His majesty will no more be terrifying to us, seeing He shows Himself a Father towards us in the person of His only Son. We see then that St. Paul’s intention is to keep us close to Jesus Christ.
And therein we also see what our perversity is. For it is certain that the care and zeal which St. Paul had, to make us cleave steadfastly to the Son of God, came through the wisdom of the Holy Spirit, who knew our frailty and inconstancy. If we had (in a manner of speaking) one drop of sound sense, it would be enough to make us understand that by the gospel we may possess God’s Son who gives Himself to us, and that by having Him, we have all we can ever wish for.
It would have been enough to have spoken this in one word, as St. Paul has shown already, (Rom. 8:32) but we see how he repeats and confirms his saying, as though it were hard to believe. And indeed it is hard, because we are too much given to distrust and unbelief. Again, to believe for one day is not all that we have to do.
It is necessary for us to persevere, which is found as a very rare thing in this world, because we are always fluttering about, by reason of which men, as it were, willfully deprive themselves of what was given them. Furthermore, since all the world is in this case, and we cannot be won or persuaded without great pains to come to our Lord Jesus Christ and to rest on Him, let us use the remedy St. Paul proposes here.
And first of all we must carefully observe that Jesus Christ is the door to open heaven to us, (John 10:9) for we know that at His death the veil of the Temple was rent in two, (Matt. 27:51) and that in such a way, that we may now enter without inhibition into the sanctuary of God—not of such a material temple as was then— so that we may approach into the presence of our God and come to Him for refuge, just as a child throws himself into the lap of his father or mother, for it is certain that God surpasses all the fathers and mothers of the world in all kindness and favour.
Seeing then that we know that, what more do we think would be to our benefit? What better or more excellent thing would we have rather than God? Then we must go and search for it in the bottom of hell. For when we have engaged in wanderings to our heart’s content we shall invariably find that there is nothing in any of all the creatures high or low that is worth a straw in comparison with God, as the prophet Isaiah says. (Isaiah 45:6)
So then, seeing that God has given Himself to us in the person of our Lord Jesus Christ, and that the whole fulness of the Godhead dwells in that great sanctuary which was typified by the visible sanctuary of the law, (Hebrews 9:9) ought we not to be fully satisfied when we have that, and to rest ourselves wholly there?
And although our minds and our affections are fickle, yet they ought to be held in check like prisoners, so that we may say, ‘Let us cleave, let us cleave to our God,’ according to that saying of David, ‘Behold, all my happiness and all my joy is joined to my God! (Psalm 73:28) He is the fountain of light and life. (Psalm 36:9) He is my portion, I cannot have a better lot, I must take all my delight in Him.’ (Psalm 16:5)”
–John Calvin, “Sermon on Ephesians 3:9-12,” Sermons on the Epistle to the Ephesians (trans. Arthur Golding; Carlisle, PA: Banner of Truth, 1562/1973), 266-268.