For in the multitude of dreams and many words there are also divers vanities. The Hebrew is literally, For in multitude of dreams, and vanities, and many words; i.e; as Wright puts it, "In the multitude of dreams are also vanities, and (in) many words (as well)."
Koheleth sums up the sense of the preceding paragraph, Ecclesiastes 5:1-6. The popular religion, which made much of dreams and verbosity and vows, is vanity, and has in it nothing substantial or comforting.
The superstitious man who puts his faith in dreams is unpractical and unreal; the garrulous man who is rash in his vows, and in prayer thinks to be heard for his much speaking, displeases God and never secures his object.
Ginsburg and Bullock render, "For it is (it happens) through the multitude of idle thoughts and vanities and much talking," the reference being either to the foolish speaking of Ecclesiastes 5:2 or to the wrath of God in Ecclesiastes 5:6.
The Septuagint rendering is elliptical, ὅτι ἐ πλήθει ἐνυπνίων καὶ ματαιοτήτων καὶ λόγων πολλῶν ὅτι σὺ τὸν θεὸν φοβοῦ. To complete this, some supply, "Many vows are made or excused;" others, "There is evil."
Vulgate, Ubi multa aunt somnia, plurimae aunt vanitates, et sermones innumeri.' The Authorized Version gives the sense of the passage. But fear thou God. In contrast with these spurious forms of religion, which the Jews were inclined to adopt, the writer recalls men to the fear of the one true God, to whom all vows should be performed, and who should be worshipped from the heart.