'Shadow' in the Bible

Because many words lead to pointlessness, how do people benefit from this? 12Who knows what is best for people in this life, every day of their pointless lives that they pass through like a shadow? Who informs people on earth what will come along after them?

For who knoweth what is good for man in this life, all the days of his vain life which he spendeth as a shadow? for who can tell a man what shall be after him under the sun?

But it shall not be well with the wicked, neither shall he prolong his days, which are as a shadow; because he feareth not before God.