Ecclesiastes in not New Testament truth. It is simply a declaration that all human works done by the natural man are VANITY. It makes no reference to all the works done by those who are spiritual men and serving Christ. It is interesting that the cults love to quote their false teachings from Ecclesiastes, but ignore New Testament truth.
do all the scriptures speak of Christ, or not?
then where is Christ in Ecclesiastes?
maybe we should look for Him there, instead of dismissing it