Bede the Venerable
Catena Aurea · Lukasevangelium 17
Lk 17, Verses 20–21English original
And when he was demanded of the Pharisees, when the kingdom of God should come, he answered them and said, The kingdom of God cometh not with observation: Neither shall they say, Lo here! or, lo there! for, behold, the kingdom of God is within you.
Or the kingdom of God means that He Himself is placed in the midst of them, that is, reigning in their hearts by faith.