While studying for an upcoming sermon series on the kingdom of God, I came across this gripping description of Jesus’ invitation to the kingdom from Old Testament scholar John Bright:

Christ, then, has come to call men to his Kingdom. His mission was not to instruct men in a better and more spiritual ethic, to impart to men a clearer understanding of the character of God, to attack those abuses which had made the Jewish law the stultification of the religious spirit and to suggest certain emendations to that law—in short, to point men the way to be better men. All this he did, indeed, and with a vengeance. But he did it in the dazzling light of the coming Kingdom. His was a call of tremendous urgency, a call to radical decision for that Kingdom. The Kingdom is right there, ‘at hand.’ It stands at the door and knocks (Luke 12:36; cf. Rev. 3:20). Who will open and let it in? Who will say Yes to its coming? Over and over again in the Gospels comes the radical urgency of its call. It is a pearl of great price; you sell everything you have to get it (Matt. 13:45-46). You leave father and mother, wife and family, as if you hated them, at its beck (Luke 14;26). It transcends all earthly concerns (Matt. 6:33). If it were a question of gouging out your eye and entering it blind or having two eyes to be excluded from it, you would without hesitation mutilate yourself in order to get in (Mark 9:47). No call to be trifled with, this—like the man who puts his hand to the plow and then turns back (Luke 9:62)! No call to be answered with a modicum of moral improvement, a burst of zeal, a few New Year’s resolutions to live a better life! It is  call to total and radical obedience, to an utterly impossibly righteousness, to be perfect as God is perfect (Matt. 5:48): in short, a call to the righteousness of the Kingdom of God to which no man can attain, yet to which he may give the answer of faith. For to say Yes to the Kingdom and to submit to its rule is faith (Mark 1:15; cf. Rom. 3:22). And it is of faith’s nature to cry, ‘Lord, I believe; help thou mine unbelief’ (Mark 9:24 KJV).

[From John Bright, The Kingdom of God (Nashville, TN: Abingdon, 1953), 219-220.