St Paul in 1 Corinthians says,"I treat my body hard and make it obey me". Suppose you have been to South Korea and participated in their pre-dawn devotional practices, then you will understand what many South Koreans do daily.
You link that experience to what St Paul meant when he said, "I treat my body hard and make it obey me". Contextually, this means one gets out of bed early, prays, reads holy Scriptures, meditates, and goes to Mass.
St Paul encourages us by saying, "You must run in the same way (like the runners at the Greek stadium) ... to win" (v 24) because "that is how I run, intent on winning; that is how I fight, not beating the air" (aimlessly; v 26) - live a disciplined and purposeful life.
For St Paul, this way of life also meant being engaged with that which God has called us to be. For him, it was "preaching the Gospel", making himself "the slave of everyone to win as many as I could"; and being "all things to all men to save some at any cost ... for the sake of the Gospel" (vv 16, 19, 22-23).
God has chosen each of us for one or more special undertaking/s for God's Kingdom. It is not something to boast about or, after completing it, to receive a reward - as St Paul has clarified (vv 16-18). God has called for us to do what is a "duty" laid on us, a "responsibility" that God has put into our hands.
Lord, help us encourage one another to fulfil our vocation, individually and corporately.