Many are perplexed as to how the Reformed can tie OT circumcision with NT baptism and how infant baptism, practiced by the universal Church of Christ for 1500+ years prior to Anabaptism, is biblical, both on theological and exegetical grounds.
The fretting will cease (at least it must for the thinking Christian!) after one goes through this essay by Rev. Professor-Emeritus Dr. Francis Nigel Lee, entitled, From Circumcision to Baptism "Circumcised...in Baptism" – Colossians 2:11-12 (Biblical refutation of the baptismal views of Baptists and Anabaptists).
The material can be accessed here or here.