Jamieson, Fausset and Brown on Genesis 17:10

10. Every man child among you shall be circumcised--This was the sign in the Old Testament Church as baptism is in the New, and hence the covenant is called "covenant of circumcision" (Ac 7:8; Ro 4:11). The terms of the covenant were these: on the one hand Abraham and his seed were to observe the right of circumcision; and on the other, God promised, in the event of such observance, to give them Canaan for a perpetual possession, to be a God to him and his posterity, and that in him and his seed all nations should be blessed.