"Baptism functions in relationship to the new covenant in Christ in a manner analogous to the function of circumcision in the Abrahamic Covenant. In a word, baptism has the same symbolic significance in relationship to fellowship with God as did circumcision.
This is not to say that the two signs are equivalent in every respect. The one signified a promise in embryo that was given to a man, to his family and his nation. The other signified a promise now fulfilled in Christ and extended to people throughout all the nations of the world. The signs belong to different epochs of redemptive history. Thus circumcision by its very nature indicated the restrictions and limitations of the old covenant (because it was administered only to male seed). Pentecost - and with it baptism - marked an epochal transition, breaking down gender distinctions that were peculiar to the Old Testament so that now the new sign had no gender restriction.
Yet with respect to their distinctive covenants and epochs, both baptism and circumcision share the same core symbolism. Both point to the same promise and to the same regenerative divine indicative [PG: that is what God does for us] and conversion response imperative [PG that is what we do in response] arising from that promise both prior to and in the light of its fulfillment in Christ."
Rev Dr Sinclair Ferguson