Samādhi involves concentrating the mind upon the supreme cause of all, even if one is unaware of whether His actual nature is personal, impersonal or localized. Concentration of the mind on the Supreme is certainly a form of devotional service. To cease from personal sense endeavors and to concentrate on the supreme cause is a sign of self-surrender, and when self-surrender is present, that is a sure sign of devotional service. Each and every living entity needs to engage in devotional service to the Lord if he wishes to understand the ultimate cause of his existence.