Krishna draws a firm line here. Three kinds of action must never be given up: yajna (dedicated offering), dana (selfless giving), and tapas (disciplined living). These are not optional. They are compulsory — karyam eva, they must be done.
Why? Because these three acts purify even the wise. They are not rituals performed for show or rewards. Yajna means dedicating your effort to something larger than yourself. Dana means giving without expecting anything back. Tapas means living with discipline, choosing what is right over what is easy.
This is Krishna's answer to those who think renunciation means doing nothing. The Gita says the opposite: keep acting, but act in a way that cleanses you from the inside.