By "the kingdom of God" is meant the same thing as "the kingdom of heaven," that is, the internal kingdom set up in the heart by the power of the Spirit—that kingdom which shall stand for ever and ever, and last when time shall be no more. This the Lord calls a mystery. And if it is a mystery, it will have these three marks; it will be beyond nature, sense, and reason, will be hidden from the wise and prudent, and will be revealed unto babes.
Let us see if we can find these marks belonging to the kingdom of heaven set up in the heart. It certainly is above nature, sense, and reason, that God should dwell in a man's heart, as the Apostle says, "Christ in you, the hope of glory;" and again, "Ye are the temple of the living God; as God hath said, I will dwell in them, and walk in them" (2 Cor. 6:16). That God should take up his abode in a man's heart; that Christ should be in a man; and the Holy Ghost should make the body of his saints his temple; how can nature, sense, and reason understand such a mystery as this?
When one of the ancient martyrs, I think it was Polycarp, was brought before Trajan, when the Emperor asked him his name, he answered, "I am Polycarp, the God-bearer, for I carry God in me!" At this answer the Emperor laughed, and said, "Let him be thrown to the wild beasts." That was the only answer a persecuting tyrant could give. That a man frail and feeble, whom a lion could tear to pieces in a few moments, carried God in his bosom!—how could the wise and prudent Trajan believe a thing so unheard of? Yet it is a mystery revealed to babes; for they receive it in the love of it under divine teaching, as one of the mysteries that God the Spirit makes known in the heart.