"Our true life and task lie at least partly elsewhere, in the spiritual realm, which has no intrinsic connection to the visible world. Spirituality, the cultivation of that realm, is helped by at least some degree of detachment from the visible world."
Otherworldalism's forms include all classical Buddhism, all Puranic Hinduism, Platonism, Kabbalah and some other forms of Hellenistic Judaicism, much Christianoidity, and the Sufi form of Islam.
Otherworldalism believes that alongside the visible world is an otherworld, an invisible, immaterial "spiritual" (or "religious") world. It supposes that the true life of (at least some) humans lies (at least partly) in an immaterial "true self", detachable from the human body but temporarily attached to it, capable of experiencing the otherworld through contemplation. This unit is sometimes called in English a "soul" or "spirit", though each of these words is also used in other senses.
To Judaicists and Christianoids the answer is simply that this belief was imported from Hellenism (and ultimately from further East) and conflicts with both Tanakh and New Testament.
More broadly, perhaps the most effective response to this belief is that its adherents are never consistent.
For instance Buddhists, having declared in the first three "Noble Truths" that intention as such is the source of the problem, immediately, in the fourth, urge us to adopt "right intentions". Having declared life itself to be suffering, they proceed to urge us to live well, that is, to act rightly in the world. They constantly smuggle, into their discourse, doctrines contrary to their declared ones.
Similarly, Puranists claim to seek moksha (escape) but also affirm dharma, artha and kama (virtues to practise in the world).
And likewise for all the others. Life itself rejects this doctrine, and nobody really believes it.
Back to Our Task as Humans.