Protein is important if you want to build or maintain muscle mass. Maintenance level is about 0.7-0.9 grams of protein per pound of lean body mass (LBM). Your LBM is your weight in pounds minus the fat, so if you weigh 150 pounds and have 20% bodyfat, then your LBM is 120 pounds (150 x .8). To build muscle you need on the order of 0.9-1.2 grams of protein per pound of LBM plus resistance type exercises.
Meat, fish, poultry, eggs, and dairy are your best sources of complete protein (they contain all of the necessary amino acids in the proper ratios). Plus they contain fat that is necessary for proper digestion of the protein. It is ok to supplement with whey protein shakes (stay away from that soy) occasionally, but the majority of your protein should be coming from animal products. One ounce of meat contains about 7 grams of protein and one large egg contains about 6 grams of protein.
The tragedy of science is the slaying of a beautiful hypothesis by an ugly fact. T H Huxley