Thereupon Shriji Mahãrãj asked, "Which is the most difficult of all spiritual endeavours?"
The brahmachãris, sãdhus and householders answered according to their own understanding, but none could give a satisfactory reply.
Shriji Mahãrãj then said, "Allow Me to answer. There is no spiritual endeavour more difficult than to continuously engage one's mind on the form of God. The scriptures state that there is no greater attainment for a person whose mind's vrutti is constantly focused on the form of God, because the form of God is like a chintãmani. Just as a person who possesses a chintãmani attains whatever he desires, a person whose mind's vrutti is constantly focused on the form of God can instantly see, if he so wishes, the forms of jiva, ishwar, mãyã and Brahma. He can also see Vaikunth, Golok, Brahmamahol and the other abodes of God. Therefore, there is no spiritual endeavour more difficult nor is there any greater attainment than to continuously engage one's mind on the form of God."

[Gadhadã I-1]