We delight when what we love (our good, our perfection) is with us.
When we love another, we delight when our beloved has his good.
Now, those who have charity love God.
But God is always Infinitely Good and Perfect, Resplendent in Communion, Truth, Beauty, etc.
Hence, if you love God, you always have reason for joy.
But being joyful is good for the soul and even the bodily health.
Hence, be good to yourself: Love God.