My father-in-law was the same way. Lutheran, but never went. Diagnosed with cancer in August 4 years ago. A 6 months before he died, I asked him about his faith, salvation, etc. He wasn’t sure of any of it. After prayer and discussion, a month before he died, he declared belief.
Praise GOD!
Doesn't it make you feel great to think in some small measure the LORD used you to bring one of his sheep to the fold.