An instance showing the difference between an act of omission and the commission of an act is the difference in withholding the truth and voicing a lie. Both an act committed and an act of omission can change the result of a circumstance.
An act of omission and an act of commission are ethical issues of both a secular and religious nature. There is a difference in moral theology between formal cooperation and material cooperation both with and without consent. When a person either aids in an evil act or does nothing to prevent that act, it is cooperation with evil.