Bhagavad Gita, Chapter 12, Verse 8

Fix your mind on Me only, place your intellect in Me: then you shall no doubt live in Me hereafter.

Two real, specific instructions are given here, not one vague call to be devoted.

Fixing the mind and surrendering the intellect are named as two distinct real steps, not interchangeable. Together they're described as enough to guarantee the outcome, no doubt left attached.