Paul wrote to Christians who were being lured back into legalistic religion in which you only get what you achieve yourself.  He used the story of God’s promise to Abraham that he would have a son (Genesis 15:1-6).  The narrative goes like this: Abraham and Sarah could not have children.  Although God had promised that they would have a son, the couple agreed that Abraham would sleep with Sarah’s servant, Hagar, and the child could be brought up as his heir (Genesis 16:1-4).  However this brought great unhappiness to Sarah and Hagar (Genesis 16:5-6).  But Abraham loved his son, Ishmael, and hoped that he would inherit God’s blessing (Genesis 17:18).  However, God fulfilled His promise that Sarah would have a child, Isaac (Genesis 17:19-21).

Abraham’s dilemma was: would he give his first-born Ishmael the birthright and let Isaac have second place in the inheritance, or would he send Ishmael away and give Isaac the place God had promised him?  Genesis 21:1-21 gives the answer.  Sarah’s barren grief gave way to joy, but Hagar’s ridicule precipitated her exit from the family along with Ishmael.  It had been a tortuous roller-coaster of emotions which would have long term repercussions.  

If Abraham had waited for God to give what He had promised, the horrible family disturbances would not have happened.  Instead, he thought that the only way God’s promise could be fulfilled was by taking the matter into his own hands.  That was the same problem in the Galatian churches.  Paul was saying that they simply needed to receive Jesus as their Saviour and trust Him to change their hearts, attitudes and behaviour (Ezekiel 36:26; Philippians 2:13): instead, they thought that God would only accept them if they could achieve holiness by following all the Old Testament rules.
 
How often do we decide that God cannot be trusted to do what is needed by the time we determine is right?  Like Abraham, we may say we believe God’s promises, but also be so impatient that we solve the problem ourselves.  People do that with salvation: they think that they must work hard to be good enough for God – but they are wrong.  God has promised salvation freely to all who believe in Jesus.  In the same way, some believers make the same mistake in their walk with Christ.  They would rather do something that is inadequate themselves, than trust the Lord to lead them in what is completely right.  Trusting in the Lord often means waiting; and waiting will mean refusing to move ahead of His promise.