How important is joy?

"According to my judgment the most important point to be attended to is this: above all things see to it that your souls are happy in the Lord. Other things may press upon you, the Lord's work may even have urgent claims upon your attention, but I deliberately repeat, it is of supreme and paramount importance that you should seek above all things to have your souls truly happy in God Himself! Day by day seek to make this the most important business of your life." (George Mueller)

"I hold myself bound in conscience and in honor, not even to imagine that I have attained a proper knowledge of any one article of truth, much less to publish it, unless through the Holy Spirit I have had such a taste of it, in its spiritual sense, that I may be able, from the heart, to say with the psalmist, 'I have believed, and therefore I have spoken." (John Owen)