John Calvin on Acts 20:25

25. And, behold, now I know. He doth now utter that plainly which he had insinuated covertly. And we said that he did put them out of hope of his return, to the end he might more deeply imprint in their minds his exhortations. For we know what great force the words and speeches of men have which are uttered at their departure or death. Also, he would have them beware by this forewarning, that they do not depend upon his presence, and so their faith should faint through wearisomeness. The doctrine of the gospel is called the kingdom of God now again, which doth begin the kingdom of God in this world, by renewing men after the image of God, until it be made perfect at length in the last resurrection,