What is the meaning of [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.