ものだSupposed to, Should, That's the way it is

ものだ expresses general or societal expectations, e.g. 子どもは早く寝るものだ ('Children are supposed to go to bed early.') べきではない carries the opposite nuance, conveying that one should not do something based on moral or social reasoning, e.g. 人を見た目で判断すべきではない ('You shouldn't judge people by appearances.')

Both expressions use the same ものだ, with the only difference being the presence or absence of から 'because/since'. Therefore, ものだ is used at the end of a sentence to express the idea of how something is or should be. In contrast, ものだから presents a reason or an explanation for something, and is often used when justifying a certain action or situation. ものだ can also be used to express obligation, while ものだから is not used this way.

While both expressions contain もの, they are used with very different nuances. ものですから・もので offers a reason, and is often used to explain or justify one's personal actions or situation, e.g. 忙しかったものですから 'I was busy, so...'. In contrast, ものだ is used to express a natural tendency or general truth, e.g. １２月は仕事が忙しいものです ('Work is busy in December.', implying that's just the way it is).

Both express what should be done, but with different nuance. ことだ is used to give firm advice, e.g. 諦めずに続けることだ ('You should keep going without giving up.') ものだ expresses general expectations or norms, e.g. 仕事は地道に頑張り続けるものだ ('One is expected to keep working steadily.')

Both express what one 'should' do, but with different nuance. べき reflects personal or moral judgment, e.g. 約束は守るべきだ ('You should keep your promises.') ものだ conveys social or cultural expectations, e.g. 子どもは早く寝るものだ ('Children are supposed to go to bed early.')

はずだ conveys a specific expectation or prediction based on current evidence, like 雨が降るはずだ ('It should rain.'). ものだ expresses a general rule or common tendency, like 雨は春によく降るものだ ('It often rains in spring.'). The former is situational, while the latter is habitual or cultural.