I think I see your objection, that our decision calculation is not purely from the brain, like doing math?
Roman 10:8-11 lays it out pretty plainly,
“But what does it say? “The word is near you; it is in your mouth and in your heart, that is, the message concerning faith that we proclaim: If you declare with your mouth, “Jesus is Lord,” and believe in your heart that God raised him from the dead, you will be saved. For it is with your heart that you believe and are justified, and it is with your mouth that you profess your faith and are saved. As Scripture says, “Anyone who believes in him will never be put to shame.”
So the “heart” is more than just a math/brain calculation. It’s the totality of knowledge, experience, motivations, and conscience, being ultimately directed by conscious intentional will.
Paul says earlier in the chapter that he testifies that Israel had a zeal for God, but didn’t combine that with “knowledge”. You can probably teach us that that word “knowledge” means more than book learning of information. More thorough and intimate.
Then we have to add in the witness of the Spirit bringing conviction to our hearts when the gospel truth is being shared. That strong confirmation that we are hearing the truth. In that moment we become conscious of our broken, sinful self. That we are indeed undone by our own folly, and in desperate need of salvation.
God’s command is then to repent, believe, allow Him to rescue. Or reject His salvation.
If we respond from the heart (our whole inner being) and choose to believe the truth hat He offers, we are vouched safe, and adopted as sons and daughters.
Does that seem like a more accurate description? With our intentional will, we decide, it’s best for me to become a believer. God already did all the work to make that a possibility, my only part is to believe it from the heart.
And then my responsibility is to walk the walk of truth, as revealed by His Spirit and His Word. Again, a decision of the intentional will from the heart - daily!