The Worship of The Formless – Bhagavad Gita Chapter12 Verse5
अव्यक्ता हि गतिर्दु:खं देहवद्भिरवाप्यते || 5||
klesho adhikajara stesaamavyaktaasakta chetasaam
avyaktaa he gatirdoohkham dehabadbhir baapyate
(Bhagavad Gita Chapter12 Verse5)
The worship and meditation on the formless aspect of God by the people who are attached to the physical body and the mind is very difficult, strenuous and too much hard work. Because, the people who identify themselves with the physical body and the mind, find it troublesome to conceive and understand the formless spirit.