It's not about only "thinking" you believe as though it's something you've conjured up.
It's about truly believing.
The same way you believe the sun will come up tomorrow...if you believe Jesus has taken your sins you have been blessed with salvation. Calvinism is in effect for mainly this purpose...assurance for the saved. Its primary purpose was never condemnation for the lost though it's often twisted out of shape to distort that.
And BTW it's not your belief that saves you. It is Christ. The belief (faith) in Him and what He has done is the proof that you are a child of God.
re: “And BTW it’s not your belief that saves you. It is Christ. The belief (faith) in Him and what He has done is the proof that you are a child of God.”
Yes, according to Calvinism, there is nothing you do that saves you. It is all God’s choosing.
Your saying you believe does not save you, your thinking you believe does not save you, your belief that you believe in God’s Word does not save you. God chooses by His will who will be saved. The problem is - you don’t really know whether you are saved or not because you have nothing to do with salvation.
Sooo, how do you KNOW that you REALLY believe? Maybe you’re in the club and maybe you’re not.
I believe God’s Word is the source of our security. God promised that if we accept/believe/place our faith in His Son, and receive Him into our heart as our Lord and Master, then He would save us - we become one of His children, born not of human flesh, born not by our power or ability because we are helpless to save ourselves by our own righteousness, no, we are saved by the reliability of God’s Word, by the graciousness of His Will that all men should come to the saving knowledge of God (even though all won’t by their unbelief).
We rely on the absolute surety and promises of God. It is God’s promises in His Word we rely on, not our emotion, not our thoughts, not some vague hope that we have been “chosen”.
If we have nothing to do with receiving, through free will, God’s gracious gift of salvation to us, then you ultimately have no assurance whether you are saved or not, because any measure you use to determine whether you really believe is from within your own mind. And, we know that the mind of man is flawed so maybe you just think you’re saved. You wanting to be saved or thinking you are saved is irrelevant in the Calvinist view. If you’re chosen you’re in. If not you aren’t.
If unborn infants are already chosen to heaven or hell by God’s sovereign choice (according to Calvinisms view), then what makes you think you personally know whether you are saved or not?