I said in mine heart, Go to now, I will prove thee with mirth, therefore enjoy pleasure: and, behold, this also is vanity.
I said in mine heart. "I" (Heb., ani) is emphatic: I who had such ample opportunities of testing earthly goods, and who am now giving the results of my experience. The address to his own heart is alluded to in Jesus' parable of the rich fool, who addresses his own soul (Luke 12:19). So "(It is) mad," or rather, 'Thou art mad,' answers to God's address to him, "Thou fool" (Luke 12:20). Compare Ecclesiastes 2:19 here with "whose shall those things be which thou hast provided?" and Ecclesiastes 2:1 with "be merry."
I will prove thee with mirth - joy flowing from, possessions and pleasures.
Enjoy pleasure - literally, 'look into good;' my heart, I will test whether thou canst find that solid good in pleasure which was not in 'worldly wisdom.' But this also proves to be "vanity."