saying

No man can serve two masters.

commitment

suggests that

If people divide their attention or efforts between more than one professions or goals, none of them will be done properly; Nobody can be committed to two different causes, organizations or employers, at the same time.

Related

The complete

Also

saying of Jesus: “No man can serve two masters: for either he will hate the one, and love the other, or else he will hold to the one, and despise the other.