The apostle takes this metaphor from athletics. He advises Timothy that, if he is striving to win in his ministry, he will not be crowned unless he disciplines himself to follow the rules.
In games (whether it is a card game, croquet out in the backyard, basketball, or whatever), one is often confronted with the opportunity to bend or to break the rules. The player must discipline himself, or face the penalties - or even find himself disqualified. If one breaks the rules in football, he receives a 5-yard, 10-yard, or 15-yard penalty. In some games, the rule-breaker just gets thrown right out! The athlete, then, must discipline himself.
Yet, Paul is using this in regard to members of God's church. If we desire to be crowned, we will have to strive within the rules. We will have to discipline ourselves. In Timothy's case, the rules are scattered throughout Paul's epistle to him. In terms of the Sabbath and the annual feast days, they are the only days in the entire Bible that God designates as "holy." They are part of "the rules."
God never gives His approval to Sunday, Monday, Tuesday, Wednesday, Thursday, or Friday, but only the seventh day, the Sabbath. He never gives His approval to Halloween, Christmas, Easter, and all of the other manmade holidays, but only the ones He points out to us in Leviticus 23. If we are going to strive for the mastery within the rules, they are what we will have to live with and use in the proper way.