The Upaniṣads are part of Vedic literature and explore questions about the self, knowledge, reality and liberation. Many take the form of teacher-student dialogues.
There are many Upaniṣads from different periods and schools. Ideas such as ātman and brahman are understood differently across Indian philosophical traditions.
Śrī Īśopaniṣad is among the works translated and commented upon by Śrīla Prabhupāda. ISKCON studies it from a devotional standpoint, alongside other traditions of interpretation.
New readers should identify the translator and edition rather than assuming that all schools interpret each passage alike.