1 Peter 3:1-7
Contemporary English Version (CEV)
The Bible is filled with advice for wives and husbands. The men who have been charged with leading the earthly church for the last few hundred years haven't always done a great job of reading all of it -- they have tended to stop when they got to the end of the part about the duty of the wives, ignoring their own call. Wives are called to serve their husbands just as husbands are called to serve their wives. In selflessly serving one another, the two are united in their effort to faithfully serve and honor Christ in all they do.
So what to do if they are on differing levels of faith?
Live a life that so thoroughly honors God that the beauty of the life-seeking-faithfulness will attract the other. I don't know how many people have been nagged or pestered into the Kingdom, but many more have been won over by selfless service and steadfast dedication. When you are partnered with someone who is uncertain, live an honest life that strives to proclaim Christ's selfless love in word and deed, trusting the Holy Spirit to bridge the gap.
Cover these things in prayer. We do the best we can, and in so doing we point to Christ, and the power of his outstanding love.