“That the “mere” pouring of water is not just an outward sign but it has actual effects.”
What effect?
Scripture is clear that without the shedding of blood there is no remission of sin. The sacrificial system was in effect until the death, burial and resurrection of Christ. There is nothing in the sacrificial system concerning baptism for sin; however there is in the system abolution as a sign of he putting away of things considered by the law to be impure.
John’s baptism was evidence that the candidate had fulfilled the sacrificial law for sin.
"What effect?"
The washing away of sins:
Acts:22:16: "And now why tarriest thou? Rise up and be baptized and wash away thy sins, invoking his name. "