Adam Clarke on Isaiah 61:9

Their seed shall be known among the Gentiles - Both Jews and Gentiles are to make but one fold under one shepherd, Christ Jesus. But still, notwithstanding this, they may retain their peculiarity and national distinction; so that though they are known to be Christians, yet they shall appear to be converted Jews. After their conversion to Christianity this will necessarily be the case for a long time. Strange nations are not so speedily amalgamated, as to lose their peculiar cast of features, and other national distinctions.