The scribes and Pharisees demanded a sign from Jesus. This is not because they had not seen enough miracles, but because they wanted a sign that would legitimate and authenticate Jesus' claims.
However, Jesus did not work wonders to prove Himself but to reveal the presence of God!
So, He reminded them of the sign of Jonah. Why the sign of Jonah?
Jonah was referred to show the contrast between the disbelief of the Jews and the faith and repentance of the Ninevites at Jonah's preaching.
The reference to the Queen of the South (Mt.12:42) parallels that of Jonah and what he preached in Mt.12: 41. Yet Jesus is greater than Jonah and Solomon. The scribes and the Pharisees failed to recognise this truth. They did not have the sincerity of the Ninevites or the Queen of the South.
This is true today when we refuse to see God's actions in the kind deeds of others outside the Church community. This pride takes us away from the reality of our faith and trust in God.
Micah shows us the way God asks of us:
"To act justly, to love tenderly and to walk humbly with God." (Micah 6:8)
Let us make this way our way of life!