Both Mary and Joseph came from the tribe of Judah.
The theme of the Book of Matthew - To prove Jesus is the King and the Messiah. He is the Christ. We need to rejoice that we are included in His family.
Malachi 3:14 You have said, 'It is futile to serve God. What did we gain by carrying out his requirements and going about like mourners before the LORD Almighty?'
God has rebuke the priest and Judah's people because they are unfaithful to God in their offerings, tithes and etc. So God told them to return to Him for If is the God the LORD who does not change! But in this particular verse they said: IT IS FUTILE/USELESS TO SERVE GOD! And this statement was normally used by the people today. Some will say, "you connot earn possessios or riches in serving God". But as for us, we will Serve Him faithfully! For our labor in the Lord is not in vain and it will surely be rewarded.