By being saved, the EVENT of salvation is how we get that assurance. That is when God, the Creator of everything, makes us all new giving us new life and lifting the veil through the work of His Son Jesus on the cross. Being saved is how we are assured. Being saved is more that repeating some words a pastor says, or being dunked under water. I think this is where the disconnect is with you, a misunderstanding of what salvation actually is. I understand I was in a place where I thought I was a Christian and actually wasn't, and that messes everything up when it comes to understanding the things of the Spirit. Again only God can assure you of salvation, and that happens at the point you are born again (when you are saved).
Your words, "Being saved is how we are assured.".
Me: Hey Jimbone, how do you know you are saved?
Jimbone: Because God assures me that I am saved.
Me: How can you be so assured?
Jimbone: Because God saved me.
Can you not see the circular reasoning?
In case you don't know, circular reasoning is really really really dangerous.