Is their faith in God head knowledge? They try to figure Him out, but He’s out of the box. The word says, “Great is our Lord, and of great power: His understanding is infinite,” in Psalm 147:5.
The reason he or she can’t have faith in God the Father may be because they can’t understand Him. Whereas Jesus lives in your heart (John 14:17). The heart is above the mind in Jesus’ and God the Father’s words. That’s where you truly are. That’s why God looked in David’s heart and chose him as king of Israel in 1 Samuel 16, beyond the reasoning of even Samuel the powerful prophet.
Some religions have rules that if they’re not followed it may seem irreverant. How can someone be justified of being saved by God and being in His holy family? We can’t. We are saved by faith through grace , says Ephesians 2:8.