The answer to marriage problems between Christians and, in fact, any other type of problem that the Believer might have, is found exclusively in Christ and the Cross.
Most may wonder as to how our Faith in Christ and what He did for us at the Cross can have a bearing on marriage problems? The answer is simple; it is the Holy Spirit Who makes the difference (Romans 8:2).
JSM
A marriage is a yoke.
"Be ye not unequally yoked together with unbelievers: for what fellowship hath righteousness with unrighteousness? and what communion hath light with darkness?" (II Corinthians 6:14).
There is no way to fully emphasize the fact that believers are commanded in Scripture NOT to marry unbelievers.
But in the case of being yoked . . . just consider the horses that are working together to plow a field. They are both wearing blinders.
The thing about blinders is that the horse can only look forward - and do not know that there is something on his side, for if he did know, he would be biting and fighting the other horse. Rather, the two horses are looking forward and working together.
When a husband and a wife clearly set their sights on the Lord and see His perfect plan for their lives, they don't have time to nitpick and find fault with one another.
Yes, it is possible to improve a marriage . . . a marriage that God can bless.