Here are four quotes from four different voices on themes in the Book of Matthew:

Charles Spurgeon — on Matthew’s central theme:

“Matthew’s Gospel is the Gospel of the Kingdom, and of the King.”
That captures Matthew remarkably well: Jesus is presented as the promised King, announcing and demonstrating the Kingdom of Heaven. (Christian Classics Ethereal Library)

D. A. Carson, describing R. T. France’s work on Matthew:

“Well written and judicious on both critical and theological issues.”
Carson’s observation points to something important about Matthew itself: the Gospel rewards both historical study and theological reflection, particularly regarding Jesus as Messiah, Israel, and the Kingdom. (Biblical Studies)

Robert H. Smith — on the radical grace displayed in Jesus’ parables in Matthew:

“People regularly understand and appreciate God’s strange calculus of grace as applied to themselves but fear and resent seeing it applied to others.”
That’s a particularly sharp summary of Matthew 20’s parable of the workers in the vineyard—and of Jesus’ repeated challenge to religious assumptions about who deserves God’s favor. (friarmusings)

R. T. France — on that same parable and the surprising nature of God’s Kingdom:

“No one has been cheated; the agreement has been scrupulously observed.”
France points out that Matthew 20 deliberately makes God’s generosity seem unsettling. The issue isn’t whether God is unjust, but whether we’re willing to accept His generosity toward people we think deserve less. (friarmusings)

Matthew introduces Jesus not merely as a religious teacher offering some helpful life advice, but as the King announcing a Kingdom.