"'So shall thy seed be.' In the earlier blessing (13:16) Abraham had been promised a seed like the dust of the earth for number. The change of figure now was no mere literary variation, but a significant addition to revealed truth. Here was not only an earthly natural seed of Abraham but also a heavenly community who should be his as being his spiritual seed and heirs. The promises of God included both, as Paul clearly recognized and expounded in later years: 'For they are not all Israel, which are of Israel: neither, because they are the seed of Abraham, are they all children: but, In Isaac shall thy seed be called. That is, They which are the children of the flesh, these are not the children of God: but the children of the promise are counted for the seed' (Romans 9:6-8)." ~Abraham: Father of the Faithful, p. 50