How big a factor does the Bible play in the Christian’s physical, emotional, and mental health?
This is a good and interesting question. There is no standard answer, but here are some points to consider from a Christian theological perspective.
From the point of view of Christian theology, the Bible is the foundation of all Christian knowledge. In other words, the Christian knows how to interpret the world and what God has done through the study of the Bible.
Second, the Bible is a book of grace and love. God has revealed his love to his people through the sending of his son, Jesus. According to the Christian, this knowledge leads to peace and joy. From this perspective, the Bible plays a huge role in the emotional and mental heath of a person. Moreover, Christians speak of the promises of God. Meditating on these promises also gives great peace. Mental wellness is, therefore, consistent with a high view of the Bible.
As for physical health, there is an important nuance. Physical wellness can be achieve as well, if we consider that people are holistic beings. In other words, a healthy mind promotes healthy bodies.
In short, for the Christian the Bible is central to wellness.