I think what is amazing (and maybe it’s God’s way of bringing assurance) that we CAN cite doctrinal truth as part of our testimony about being saved!
As someone said elsewhere (and as I recall the elder of the assembly I attended where I was baptized also stated), baptism is an outward sign of an inward faith. It’s the Lord’s mechanism for us to tell all the world that something has happened to this individual you see here in the water. It opens up a door for conversation (witnessing) and, yes, for ridicule and mockery from those who do not/will not believe. We thus, identify with Christ. We declare to a dying world, “I choose to live with Him!”
Amen :)