The word tribulation is very suggestive. It comes from a root which means 'a flail'.
The thresher uses the flail to beat the wheat sheaves, that he may separate the golden wheat from the chaff and straw.
Tribulation is God's threshin. Not to destroy us, but to get what is good, heavenly, and spiritual in us separated from what is wrong, earthly, and fleshly.
Nothing less than blows of pain will do this. The golden wheat of goodness in us, is so closely wrapped up in the strong chaff of sin that only the heavy flail of suffering can produce the separation!
Many of us would never enter the gates of pearl were it not for this unwelcome messenger, pain! "We must go through many troubles to enter the kingdom of God!"
Act 14:22 Confirming the souls of the disciples, and exhorting them to continue in the faith, and that we must through much tribulation enter into the kingdom of God.
~J. R. Miller~