“Neither shall they say, Lo here! or, lo there! for, behold, the kingdom of God is within you.”
Luke 17:21 — Greek Interlinear
Church Fathers on Luke 17:21
Because our Savior, in His discourses which He addressed to others, spoke often of the kingdom of God, the Pharisees derided Him; hence it is said, And when he was asked by the Pharisees when the kingdom of God should come. As though they said tauntingly, “Before the kingdom of God come, which you speak of, the death of the cross will be your lot.” But our Lord testifying His patience, when reviled reviles not again, but the rather because they were evil, returns not a…
Or, perhaps, the kingdom of God being within us, means that joy that is implanted in our hearts by the Holy Spirit. For that is, as it were, the image and pledge of the everlasting joy with which in the world to come the souls of the Saints rejoice.
Or the kingdom of God means that He Himself is placed in the midst of them, that is, reigning in their hearts by faith.