I’ve had the sneaking suspicion that’s what He meant by those words. Seems to go better with the rest of His teachings. I have imagined Jesus gesturing pointing towards His heart and then towards Thomas’s heart to emphasize His point.

To be clear, this is my own conjecture and interpretation, which is no better than anyone else’s, including the translators and early /late church leaders. But if it is true, then I am following Jesus’s words just like them. We all gotta find our own way. Thank you for the extra validation and info!