1 Samuel 16:12, 1 3 –So Jesse sent for him.  He was ruddy and handsome, with pleasant eyes.  And the Lord said, “This is the one; anoint him.”  So as David stood there among his brothers, Samuel took the olive oil he had brought and poured it on David’s head.  And the Spirit of the Lord came mightily upon him from that day on.  The Samuel returned to Ramah.
David was anointed to be king, but he would not be king until 2 Samuel 5.  The current king, Saul, loved David.  But that love would turn to jealousy, and then would turn into attempted murder.  After David’s successful battles, Saul did not like how his glory was falling onto David.  Saul feared David would overtake his throne, so for a long period of time, he hunted David down to kill him.  Instead, Saul eventually lost his life and David soon became king.
The same situation is true about the anointing God has on us as Christians.  God has a purpose on all of our lives, but we may not see it come to fruition for many years.  During the time God is developing us for our calling, we will face opposition preventing us from reaching it.  Satan knows the impact our call will have on his evil scheme and will stop at nothing to make us quit.  But if we do not lose heart, we will see it come to pass.  Remember, God is sovereign, and will see us to completion.