Generally speaking, compared to the Middle Ages, there were higher standards of living, greater economic opportunity, and higher life expectancy in the Renaissance. Within those contexts, explain a reason for the rebirth of heroic ideal and the cult of beauty.

Historians believe that the Renaissance developed in Italy partly in reaction to the Black Plague in 1348. The plague resulted in the deaths of an estimated 75 million to 200 million people, and many historians believe that the death people witnessed during the plague made them more interested in the affairs of life rather than in the afterlife. In addition, following the plague, the working class in Italy was in a better position than they had been previously, as the price of food and land dropped. As people lived better lives, they devoted themselves increasingly to matters that were not directly connected to mere survival.
The heroic ideal and the cult of beauty arose as part of the development of humanism, or the focus on human beings over spiritual matters, in Italy and other areas. Interest in Greek and Roman antiquity was part of this movement. The heroic ideal was the perfect person, and, as West writes in "Spenser and the Renaissance Ideal of Christian Heroism," the idea of a Christian hero arose in Renaissance literature after the "reemergence of the classics in the Italian Renaissance." The cult of beauty was also part of the Renaissance as a reflection of the growing belief in celebrating the physical rather than the purely spiritual. This belief also was inherited from the Greek belief that beauty was an ideal that could be expressed in physical things. 
 
Source:
"Spenser and the Renaissance Ideal of Christian Heroism." Michael West PMLA Vol. 88, No. 5 (Oct., 1973), pp. 1013-1032.