Romans 8: 28 & 29 leave no room for human error. Our sin abounds but grace abounds more. I can’t say whether or not a true born again Christian is capable of suicide, but I can say a Christian who has a dynamic relationship with Christ is incapable of suicide.
Human beings are flawed. They are incapable of being perfect. I do believe in time there is a possibility that there will be humans who do attain perfection through Christ very shortly before the Second Coming, but as a rule today, no.
I only say this because probation closes at some point, and those who will be saved will have their fate sealed. They will have been tested and thereby perfected.
The problem with our flawed nature today, is that you can be a devoted Christian 99.99% of the time. It only takes that one time when you’re devastated beyond sound mind, for you to succumb.
Sure, theoretically you can avoid sin if you’re constantly connected. That avenue is open to us. So far, only one human in history has attained that perfection, a total 100% connection with God and ultimate perfection.
We sin. At the present we cannot ‘not sin’. That’s why we needed and still need Jesus’ sacrifice. It purchased our sinful souls back.
So I hear what you are saying. In theory you’re right, but humans being the frail sinners they are, I’m not convinced you’re totally right.