This is the core of the teaching of the Bhagavad Gita. Each of the subsequent chapters in this book is an elaboration of this theme from a particular angle. The strong and the virile alone are fit for a life of great consequence. Achievements both here and hereafter are born of competence and manly action. Strength nurtures life.
Weakness wears it away.
Virtue and righteousness are the outcome of strength. It is the feeble that resort to foul play. Action born in manliness leads to freedom and its opposite to bondage. Strength and sreyas are identical. This is the teaching of the Gita.