When Christ wanted to teach his disciples how to treat each other, he realized that experiencing something is more life changing than words alone. So Jesus got up from the meal, took off his outer garments, and began washing their dusty feet - a service usually relegated to the lowliest servant. Then, based on the powerful experience they'd just shared, he taught his disciples about serving each other.
In the same way, your unbelieving spouse may need to experience Christ's love through you before he can believe it's real. If you consistently demonstrate Christ's love by serving your spouse, you appropriately give him the opportunity to experience Christ's love in a way that goes beyond mere words and religious talk.