Solomon relates his personal experience Ecclesiastes 2; the result of which was “no profit,” and a conviction that all, even God’s gifts of earthly good to good men, in this life are subject to vanity. His trial of God’s first gift, wisdom, is recounted in Ecclesiastes 1:12-18.
Was - This tense does not imply that Solomon had ceased to be king when the word was written. See the introduction to Ecclesiastes. He begins with the time of his accession to the throne, when the gifts of wisdom and riches were especially promised to him 1 Kings 3:12-13.