Take on and Take pains

Take on verb - To enter into contest or conflict with.

Take pains and take on are semantically related In some cases you can use "Take pains" instead a verb "Take on".

Take pains verb - Try very hard to do something.

Take on and take pains are semantically related in belief topic. Sometimes you can use "Take on" instead a verb phrase "Take pains", if it concerns topics such as attempt to achieve something.