When a mitzvah or a sin comes to your hand, it would be extremely beneficial to realize this aspect, but it's not easy. "Im lo achshav aymasai," if not now, when? Free will is only in the present and this moment is in your control. Since a person lives only from moment to moment, the existence in which you're living at any particular point in time is the total existence for you and all reality. By doing a mitzvah, you infuse all of existence with holiness and when you sin, you infuse all of existence with impurity.