That’s a great question.
But in some ways it’s also like saying “How do you know the wind exists? How do you know Black Holes exist or other planets? How do you know love is real and just not a chemical response in your brain?” There are plenty of things we can’t explain, but can feel or experience even.
For me, it’s been more experiencial. Most of us have a voice in our head that tells us we’re failures or screw ups when we blow it. The peanut gallery of the mind always seems to accuse us so to say. As I grew to know—and love God— another voice emerged when I would fail or mess up. It was one that told me “you’re loved despite your failures.” It would tell me it was proud of me when I fell short. That it loved me when I felt unworthy of love. That when I felt shame it wasn’t needed. That voice confounded me because all my life the voice in my head told me: do more, be a better person, strive for achievement, make people love you. Yet, here was this voice that told me I was loved as is. Your conscious just doesn’t do that.
Like I said in the article, it was a slow process, and sometimes I doubt that voice (more often than I’d like to admit), but getting to really know Jesus, his grace, and great love for me and humanity moved the proverbial quarter to drop from my head to heart. And when that happened, it changed everything.