Are all gospels the same?  Nope.  There are plenty of churches telling us that in order to meet God's entrance requirements for heaven we have to jump through all sorts of hoops and obey a multitude of rules and rituals.  What does God say in Romans chapter three?  There Paul lays out the case very clearly that guilty humans are justified/declared righteous in the sight of God by faith in Jesus Christ alone, and not by any sort of obedience to rules or rituals.  

It does indeed matter to know that you have the right Gospel message.  The margin for error is zero.