There is a sin of omission as well as of commission

Here commission is performance, and omission is non-performance. You may be acting wrongly in a certain thing; you may be equally at fault in not doing a certain thing. For example, the sin of commission is drowning a person by pushing him into the canal; the sin of omission is making no attempt to rescue him when someone else has pushed him in. Silence gives consent, so by keeping silent you have committed a sin of omission.