'Striving' in the Bible

And I applied my heart to the knowledge of wisdom, and to the knowledge of madness and folly: I perceived that this also is a striving after the wind.

For what will man have of all his labour and of the striving of his heart, wherewith he hath wearied himself under the sun?

There is no end of all the people, of all that stood before them; those however that come after shall not rejoice in him. Surely this also is vanity and a striving after the wind.

but, having suffered before and been insulted, even as ye know, in Philippi, we were bold in our God to speak unto you the glad tidings of God with much earnest striving.