Romans 4:11 – “He received the sign of circumcision as a seal of the righteousness that he had by faith while he was still uncircumcised.”
"If circumcision was for Abraham a seal of the righteousness that he had by faith, then we cannot say the cutting away of the flesh was simply an ethnic identity marker or a sign of mere physical import. Circumcision was a seal of the deepest spiritual realities, a visible sign of the forgiveness of sins and justification by faith. Just like baptism would be centuries later.
"And if this spiritual sign—a seal of the righteousness that comes by faith—was administered to Abraham and his infant sons, then we cannot say that the thing signified must always be present before the sign is administered. Isaac was circumcised, and so was Ishmael—both being given the seal of justification by faith before the exercise of faith. Just like infant baptism.
"So whether infant baptism makes sense to you or not—and I deeply respect my non-paedo friends in my church and in the broader church—shouldn’t we at least agree that the basic spiritual import of circumcision and baptism is the same and that there is biblical precedence for administering a spiritual sign without the immediate presence of the thing signified?
"Makes sense to me."