Explanation of もの as sentence final particles.
"～ものだ" is used in the cases indicated below.
1) A sentence "___A___は___B___ものだ" means "It is common / normal that ____A____ is ____B____. (Therefore, it is a matter of course.)"
人はいつかは死ぬものだ A person dies someday.
2) To emphasize a meaning of a hope / wish.
3) To express a recollection： a experience that was repeated before.
4) To express a surprise： evaluation.
5) To explain a reason/background of a specific situation which has already happened.