Is the need the call?

Growing up I often heard that the need was the call but as I studied scripture I saw over and over again that to go without the Lord sending you was disobedience.  For example in Jeremiah 14:15, "Therefore this is what the Lord says about the prophets who are prophesying in my name: I did not send them, yet they are saying, ‘No sword or famine will touch this land.’ Those same prophets will perish by sword and famine."  When Isaiah saw the need his prayer was that the Lord would send him.  He did not assume that because there was a need that he should go.  His prayer was, "Here am I, send me."  Isaiah 6:8  When Jesus saw the people He told His disciples that they would, "Ask the Lord of the harvest, therefore, to send out workers into his harvest field.”  Matthew 9:38
So how should we view the need if it is not the call?  It should lead us to pray that the Lord would send workers into the field.  We should also pray that we would be willing to go ourselves if the Lord would send us.  The need is all around us and if the need is the call then what would we do?  What need would we respond to?  Let us pray that the Lord send workers and let us pray "here am I, send me."