Two ideas, each enormous, sit packed in this single shloka. First: the person established in wisdom leaves behind both merit and sin, right here in this life. Second: yoga is karmasu kaushalam — skill in action.
Yogah karmasu kaushalam is one of the Gita's most quoted definitions. Yoga is not withdrawal. It is the art of doing things well — with presence, without clinging. Everyone performs action. The yogi performs it with skill, free from the drag of attachment.
A skilled cook uses the same ingredients everyone else has. The difference is not in the raw materials but in the craft. Likewise, all people act. The difference between ordinary action and yoga lies in how the action is performed — with equanimity, or with craving.