From: Matthew 11:11-15
The Mission of John the Baptist. Jesus' Reply
(Jesus spoke to the crowds,)  "Truly, I say to you, among those born of women there has risen no one greater than John the Baptist; yet he who is least in the Kingdom of Heaven is greater than he.  From the days of John the Baptist until now the Kingdom of Heaven has suffered violence, and men of violence take it by force.  For all the prophets and the law prophesied until John;  and if you are willing to accept it, he is Elijah who is to come.  He who has ears to hear, let him hear."
11. With John the Old Testament is brought to a close and we are on the threshold of the New. The Precursor had the honor of ushering Christ in, making Him known to men. God had assigned him the exalted mission of preparing His contemporaries to hear the Gospel. The Baptist's faithfulness is recognized and proclaimed by Jesus. The praise he received is a reward for his humility: John, realizing what his role was, had said, "He must increase, but I must decrease" (John 3:30).
St. John the Baptist was the greatest in the sense that he had received a mission unique and incomparable in the context of the Old Testament. However, in the Kingdom of Heaven (the New Testament) inaugurated by Christ, the divine gift of grace makes the least of those who faithfully receive it greater than the greatest in the earlier dispensation. Once the work of our redemption is accomplished, God's grace will also be extended to the just of the Old Alliance. Thus, the greatness of John the Baptist, the Precursor and the last of the prophets, will be enhanced by the dignity of being made a son of God.
12. "The Kingdom of Heaven has suffered violence": once John the Baptist announces that the Christ is already come, the powers of Hell redouble their desperate assault, which continues right through the lifetime of the Church (cf. Ephesians 6:12). The situation described here seems to be this: the leaders of the Jewish people, and their blind followers, were waiting for the Kingdom of God the way people wait for a rightful legacy to come their way; but while they rest on the laurels of the rights and rewards they think their race entitles them to, others, the men of violence (literally, attackers) are taking it, as it were, by force, by fighting the enemies of the soul--the world, the flesh and the devil.
"This violence is not directed against others. It is a violence used to fight your own weaknesses and miseries, a fortitude, which prevents you from camouflaging your own infidelities, a boldness to own up to the faith even when the environment is hostile" ([St] J. Escriva, "Christ Is Passing By", 82).
This is the attitude of those who fight their passions and do themselves violence, thereby attaining the Kingdom of Heaven and becoming one with Christ. As Clement of Alexandria puts it: "The Kingdom of Heaven does not belong to those who sleep and who indulge all their desires, but to those who fight against themselves" ("Quis Dives Salvetur", 21).
14. John the Baptist is Elijah, not in person, but by virtue of his mission (cf. Matthew 17:10-13; Mark 9:10-12).
Source: "The Navarre Bible: Text and Commentaries". Biblical text taken from the Revised Standard Version and New Vulgate. Commentaries made by members of the Faculty of Theology of the University of Navarre, Spain. Published by Four Courts Press, Kill Lane, Blackrock, Co. Dublin, Ireland. Reprinted with permission from Four Courts Press and Scepter Publishers, the U.S. publisher.