With this shloka, Krishna begins a ladder of practice — four steps descending from the highest to the most accessible. This is the topmost rung. Fix your mind in Me. Direct your intellect toward Me. Do just this much, and from that point onward, you will live in Me. No doubt about it.
The instruction is startlingly simple: mind and intellect, both in Krishna. When a grandchild holds a grandfather's hand while crossing a busy road, the child stops worrying about traffic and direction. The hand is enough. That is what Krishna offers here — hold on to Me with your mind and your understanding, and the rest takes care of itself.