But [whether by night or by day,] remember thy Sustainer's name, and devote thyself unto Him with utter devotion.

But keep in remembrance the name of thy Lord and devote thyself to Him whole-heartedly.

So remember the name of thy Lord and devote thyself with a complete devotion -

And remember the name of thy Lord and devote thyself to Him with (complete) devotion.

And remember the name of your Lord and devote yourself to Him with [complete] devotion.