Verses 4 through 6 tell us not to delay in paying our vow to God. It is better that we not vow than that we vow and not pay.
Verse 7 says, "For in the multitude of dreams and in many words are also vanities. Rather, fear God."
In 5:8-17 and 6:1-12 we have sundry illustrations of various things in human life that are vanity.
In a province a poor man is oppressed under the wresting of justice and righteousness, although there are ranks of officials who should attend to this matter and even there is a king who is used to doing things for the advantage of the land. This is vanity (5:8-9).
The ones who love silver and love abundance with income will not be satisfied, and the fullness of the rich will not let him sleep. This is also vanity (vv. 10-12).
The rich man keeps his riches to his own hurt, and his riches are lost in a bad venture and nothing is left for his son. He has labored for the wind, eating in darkness and having much vexation and sickness and resentment. This is a grievous evil and is also vanity (vv. 13-17).
According to 6:1-2 an evil that is heavy upon man concerns a man to whom God gives riches, wealth, and honor. God does not empower him to eat of it, but a stranger eats it. This is vanity and an evil plague.