According to a 2004 study conducted by Peter Larson and David Olson, 81% of couples who have low positive couple agreement on spiritual matter have marriages that are very low in quality. Only 15% of these couples have a terrific marriage.
Conversely, nearly half of high quality marriages have high positive couple agreement on spiritual matters while 32% of these couples have very low quality marriages.
So, positive couple agreement on spiritual matters appears to help marriages have higher quality, but even more so it appears that it buffers against low quality marriages.
It is very important to be on the same page spiritually.