Only fear Yahweh, and serve him in truth with all your heart; for consider how great things he has done for you.
In truth — Be ever honest, ever sincere; with all your heart - have every affection engaged in the work of obedience; act not merely from a principle of duty, but also from a pious, affectionate sense of obligation. Act towards your God as an affectionate child should act towards a tender and loving parent.