The sub theme of this plasy is a bout class division. Because of that we saw Nicola and louka who were belonging to the working class. but in fact, Show was arguing in his play that every human being has the right to improve his life;even those who belong to the high level in the class division like Sergius could degrade their social status by marrying, for example,the type of Louka.
So,it is not the class to which you belong that give you importance or value in life; it is his/ her experience and devotion towards certain goals he/she seeks in life and works to achieve it.
Shaw wants to promote for a certain kind of marriage: he wants to argue that love and marriage are completely different.He felt that marriage is partnership where the two parties should be really equal to each other in order to allow to this marriage to succeed. Shaw is realy promoting a kind of marriage that would last in order to give birth to a healthy generation.
By this, we can say that love and marriage are not related to each other