Fat is a metabolic burden. The fact that you have a high percentage of fat on your body means that you are walking around with a millstone around the neck. It promotes inflammation and can raise your risks of heart disease, diabetes, and stroke. It is also a sign of something more: Metabolic syndrome, a group of health problems that include too much fat around the waist, elevated blood pressure, blood sugar, triglycerides and low "good" HDL cholesterol – all boosting your risks of diseases.
Gaining lean muscle tissue, on the other hand, means that your body needs to be in homeostasis. The stable condition is the condition of optimal functioning for the organism and it depends on many variables, such as body temperature and fluid balance, being kept within a preset range. Other variables include the pH of the extracellular fluid, the concentrations of sodium, potassium and calcium ions, as well as blood sugar level. All these need to be regulated despite changes in the environment, diet or level of activity. Sounds more like a science project, but who said that gaining lean mass was easy? In fact, it is way more complicated than just lifting weights and following a high protein diet.
Shed the fat before you go all out on muscles. Anyway, your body starts by doing them simultaneously. Losing the fat is easy, gaining lean muscle is the hard part. That way, you’ll see your gains easily and you might gain muscle faster since your body will be in perfect tune to maximize the coming gains.