This is a different situation than a spiritually indifferent spouse, and it deserves its own honest treatment: two genuine believers, both sincerely walking with God, growing at visibly different speeds for a season. One is hungry for Scripture and prayer; the other is faithful, but slower, more tired, or simply in a different season of life.
Different speeds, not necessarily different destinations
God doesn't form every believer on the same timetable. A couple caring for young children, weathering a health crisis, or carrying financial strain may find one spouse has less capacity for visible spiritual growth in that season — not because their faith is weaker, but because their circumstances are heavier.
The temptation growth creates
Growth can quietly produce something ugly if it isn't watched: a sense of superiority. "I've changed — why haven't you?" may be factually accurate and still spiritually destructive, because it turns growth into a weapon rather than a gift. Genuine spiritual maturity should make a person more humble, not more judgmental of the one still catching up.
Encourage without supervising
There's a real difference between encouraging your spouse's growth and quietly appointing yourself their supervisor — monitoring, correcting, subtly announcing where they're falling short. One builds trust. The other slowly turns a marriage into a classroom neither person actually wants to be in.
Where this goes next
What matters most isn't whether both spouses are growing at the same pace. It's whether both are still, genuinely, moving toward the same Christ — and whether the one growing faster is willing to kneel beside the one still catching up, rather than standing over them.