This is the 4666th most frequent Polish word.
nadzieją
"Hope" (instrumental singular form of "nadzieja").
In this sentence, "nadzieją" (hope) is the direct object of the verb expressing a feeling or expectation about the future.
Mam nadzieję na lepsze jutro.
I have hope for a better tomorrow.
In this context, "nadzieją" serves functionally as the subject in the instrumental case to describe what constitutes the hope of people.
Nadzieją ludzi jest pokój na świecie.
Hope for people is peace in the world.
Here, "nadzieją" is used in instrumental case to indicate the manner of her coming or her mental state of optimism.