Reading Bruce Waltke's commentary on Genesis, he has a fine couple of paragraphs on page 264 where he explores how the sign of circumcision relates to baptism today. I agree with nearly everything he says, and it's so helpful that I thought I'd put it here in case it's helpful for some:
Today God defines his people not by their physical descent from Abraham but by their relationship to Jesus Christ, the only descendant of Abraham who kept God’s covenant without transgression. Moreover, God administers them by a new covenant. In this new covenant he grants his people his Holy Spirit and writes the law on their hearts, guaranteeing their circumcision (Jer. 31:31-34 – esp. v. 33; Rom. 2:28-29; 2 Cor 3:2-6; Gal 6:15). Circumcision, the old sign of initiation into the covenant community, is replaced by a new sing, baptism. This rite symbolises that the saint is ‘circumcised, in the putting off of the sinful nature, not with a circumcision done by the hands of men but with the circumcision done by Christ’ (Col 2:11). It also symbolizes that they live not naturally but supernaturally by faith, ‘having in been buried with him in baptism and raised with him through [their] faith in the power of God, who raised him from the dead’ (Col 2:12). Baptism is the symbol of inclusion in Christ’s church, the new expression of God’s covenant people, and the symbol of the cleansing of sin (Rom 6:1-14; 11:16; 1 Cor 7:14; Col 2:11-12; 1 Peter 3:20).
In the baptism ritual God continues to use the family institution (see Gen 7:1; Acts 16:31). Because in Christ’s body there is neither male nor female, all may come, male, female, parent, and child (Luke 18:15-17; Gal 3:26-29; Col 2:11-12; cf. Luke 1:59; 2:21; Phil 3:5). However, once again the community must guard against the danger of participating in an initiation rite without living the life of God’s new covenant.