这个句子很有意思，先说结果，再说原因（用分词短语表示）。

They have the incentive to develop and maintain healthy habits believing that these habits can bring enjoyment to their lives.

以后写句子，务必注意大小写和标点。

分词短语作原因状语，在句末可以不用逗号与前句隔开，在句首一般加逗号。这跟 because 从句的用法相同。由于本句 these habits 是“后指”，所以不可提前。变成从句则是：
They have the incentive to develop and maintain healthy habits because they believe that these habits can bring enjoyment to their lives.