@jlacross, you are absolutely right when you mention that the heart changes when you sincerely surrender to Jesus Christ. The biblical basis of conversion is a heart change. Without the heart change, we are blind to spiritual things (1Cor 2:14).
Ezekiel 11:19 And I will give them one heart, and a new spirit I will put within them. I will remove the heart of stone from their flesh and give them a heart of flesh.
2 Cor 5:17 If anyone is in Christ, he is a new creation; the old has passed away, behold, the new has come
John 3:3 Jesus answered him, “Truly, truly, I say to you, unless one is born again he cannot see the kingdom of God”.
In my own personal experience too, I found that soon after coming to a faith in Christ, I had an increased desire to read the Bible. I think for someone like me who had no church background growing up, the conversion process is a drastic shift. However, I have also experienced losing that initial excitement and urge to be transformed as years went by. Somehow, though I got busy with church activities, I lost focus on grace and practiced Christian behavior more out of habit rather than a vibrant relationship with God in prayer.I moved from grace to mild legalism, which I didnt notice until it started robbing me of my peace and trust in God. I lost the love I had at first as in Rev 2:4. It was only on trying to re-understand grace that I found a renewed passion.
As many people who grow up in churches may not have clear memory from childhood of their conversion, they may have forgotten about their heart change and are going through the normal struggles of growing in Christian faith. In other cases, there could be a confusion between intellectual assent to Christian doctrine and actually trusting Christ. Only to those who believe and receive Christ are considered as children of God ( 1John 1:12). I think the initial heart change serves as a confirmation of our faith when we are new believers but later on we are tested to put away our old selves willingly in order to mature in our faith.
Does this strike any further questions? God bless your bible studies!