From Michael Ramsey’s God, Christ, and the World (p. 85):
So the righteousness of Jesus is the righteousness of a Godward relationship of trust, dependence, receptivity. It is a terribly hard kind of righteousness. It is sometimes hard because it involves the calls of sacrifice and self-renunciation which Jesus gives. But it is more often hard because of the shattering generosity of God, demanding an utterly childlike receptivity. To receive like a little child an unmerited gift and to be humbled in the receiving time and time again: such is the righteousness of the kingdom. It follows that in Christian ethics humility has a continuing place which throughout history secular forms of ethics find very hard to understand. It also follows that St Paul’s teaching about justification by faith, the doctrine of being right with God on the basis of God’s own gift, is in a true line with the ethics of Jesus.