There are at least two ways to try to explain why religious people get divorced less than others. One explanation is positive and the other is negative.
On the negative side, we can say that people who are religious are pressured into staying married. If both members of the couple are religious, they might belong to a church and/or to a circle of friends and acquaintances that will strongly disapprove of divorce. This will cause them to feel that they have to stay married regardless of what they would prefer to do.
On the more positive side, people who are religious might have better relationships with one another. They might be motivated to stay together by their shared faith. They might care more about one another because they feel that they have actually been sealed together by God and not simply by the edict of the government. They might be less selfish and more willing to work together because of these things. In other words, they might simply care more about making their relationship work than people who are not religious and see no real moral dimension to their relationship.
The lower divorce rate among religious people might be explained by either of these types of factors or by a combination of them.