Great point.
When faced with those who believe we can lose our salvation, I’ve found a couple of points worthwhile to communicate.
1) God knows everything in eternity future from eternity past. When He gave salvation to each believer, He wasn’t having a senior’s moment and went, DOH!!!!, I forgot about that sin.....
2) The very act of thinking we can lose our salvation ONLY happens if we are NOT thinking through faith in what Christ performed on the Cross. Our salvation is based upon our faith/believing in Him and what He provided on the Cross,...He was judged for ALL our sin. (If this isn’t understood, consider it a test,....try it though not needed, those who believe we can lose salvation are already out of fellowship, so it can be pointed out to them for them to consider it, to wake up and return back to faith in Christ.)
3) The issue being confused is salvation and fellowship. Once we are saved, we have been forgiven our sins. If we sin again, we can return to Him by facing back to Him, remembering what He Provided on the Cross and confess those sins to Him. He is sure and just to forgive those sins and we are back in fellowship.
4) When we sin, we simply fall out of fellowship. We are not condemned again. Our goal is to return to fellowship, so we might follow the Plan He has made for us from eternity past. It isn’t the believer’s goal to constantly accuse. That is the thinking pattern of the Adversary.