Earlier today, I posted some rumbles about the starling passage. After further thoughts on it, and being influenced by Hegel's dialectic, I postulate that the author of Matthew was explicitly responding to St. Paul's idea of justification.
St. Paul wrote his epistles, especially Galatians and Romans, between 49-64 A.D. In both epistles, he expounded his understanding of salvation and the relation between the converted Jews and the converted Gentiles. And if the gospel of Matthew was written between 65-90 A.D, and if the gospel had the Jews as the intended immediate readers in mind, then the author could be addressing some post-Paul issues among the Christian Jewish community.
And if that is true, then the portion in Matt 12.24-37 will be Matthew's direct response to St. Paul's theology of justification. And with the reference to Matt 12.24 ("Pharisees"), the author probably primarily had St. Paul in mind.