Gems from Schweitzer

"The Kingdom of Heaven must however be understood 'according to Jewish ways of thought.' Neither Jesus nor the Baptist ever explain this expression; therefore they must have been content to have it understood in its known and customary sense. That means that Jesus took His stand within the Jewish religion, and accepted its Messianic expectations without in any way correcting them. If He gives a new development to this religion it is only in so far that He proclaims as near at hand the realisation of ideals and hopes which were alive in thousands of hearts. There was thus no need for detailed instruction regarding the nature of the Kingdom of Heaven; the catechism and confession of the Church at its commencement consisted of a single phrase. Belief was not difficult: 'they need only believe the Gospel, namely that Jesus was about to bring in the Kingdom of God...

As there were many among the Jews who were already waiting for the Kingdom of God, it was no wonder that in a few days, nay in a few hours, some thousands believed, although they had been told only that Jesus was the promised prophet...

Jesus must have known, too, that if the people believed His messengers they would look about for an earthly deliverer and turn to Him for this purpose. The Gospel, therefore, meant nothing more or less to all who heard it than that, under the leadership of Jesus, the Kingdom of Messiah was about to be brought in. For them there was no difficulty in accepting the belief that He was the Messiah, the Son of God, for this belief did not involve anything metaphysical. The nation was the Son of God; the kings of the covenant-people were Sons of God; the Messiah was in a pre-eminent sense the Son of God. Thus even in His Messianic claims Jesus remained 'within the limits of humanity.'" 

Albert Scweitzer, The Quest of the Historical Jesus: A Critical Study of its Progress from Reimarus to Wrede (The John Hopkins University Press, 1968), 16-17