>>Now no chastening for the present seemeth to be joyous, but grievous: nevertheless afterward it yieldeth the peaceable fruit of righteousness unto them which are exercised thereby. Hebrews 12:11 (Read all of Hebrews 12) King James Version <<
In english: No discipline seems pleasant at the time, but painful. Later on, however, it produces a harvest of righteousness and peace for those who have been trained by it.
In even more plain English: Sit still you little Ba@#$rd; you will thank me in the morning.