What is the relation between wellness and disease prevention?

Solid ground. Wellness - our good health - is the solid ground that we stand on. Imagine running on rocky ground or quicksand. Easier to get hurt and we don't get as far, right? It's no accident that eating right, exercise, solid sleep, work/play balance keep us well and prevent things like heart disease, stroke and cancer.
Requires effort! Wellness and Disease prevention require significant physical and mental effort. The reason is that it requires a balance of what we eat, how we interact with the environment and how we go about our business. Excess of any of of these factors, can lead to disease. Therefore, being well means our body is operating optimally such that we prevent things from going wrong, and developing a disease. .