This verse is quoted from Śrīmad-Bhāgavatam (12.3.52). At the present moment in Kali-yuga there are many false meditators who concoct some imaginary form and try to meditate upon it. It has become fashionable to meditate, but people know nothing about the object of meditation. That is explained here. Yad dhyāyato viṣṇum. One has to meditate upon Lord Viṣṇu or Lord Kṛṣṇa. Without referring to the śāstras, so-called meditators aim at impersonal objects. Lord Kṛṣṇa has condemned them in the Bhagavad-gītā (12.5): kleśo ’dhikataras teṣām avyaktāsakta-cetasāmavyaktā hi gatir duḥkhaṁ dehavadbhir avāpyate “For those whose minds are attached to the unmanifested, impersonal feature of the Supreme, advancement is very troublesome. To make progress in that discipline is always difficult for those who are embodied.” Not knowing how to meditate, foolish people simply suffer, and there is no benefit derived from their spiritual activities. The same idea expressed in this verse from Śrīmad-Bhāgavatam can be found in the following verse from the Viṣṇu Purāṇa (6.2.17), Padma Purāṇa (Uttara-khaṇḍa 72.25) and Bṛhan-nāradīya Purāṇa (38.97).