I think it is important to understand that this word in Matthew translated "violent" is only used in the book of Matthew. Every book in the New Testament has seven words unique to that book not used in any other New Testament book. So these seven words give us a picture of what the unique agenda of each book of the Bible.
Obviously Matthew, Mark and Luke have quite a bit that overlaps between them. However, I would say you can make a strong case from the Bible that these three synoptic gospels have three specific audiences that they are describing and Matthew is describing the nation of Israel. The word really means forceful, but could also be understood as violent.
Now the term "suffereth violence" is used twice, both in Matthew and in Luke.
Here is what Luke says
"The law and the prophets were until John: since that time the kingdom of God is preached, and every man presseth G971 into it."
So obviously every man who is saved must "press into the kingdom" and the term certainly does not mean illegitimately. It is a battle to be a Christian that is fully given to the Lord. If that is not your experience then something is wrong. Matthew identifies the nation of Israel as these "violent" men. But that could also be translated as "forceful men". Abraham was a forceful man. Jacob wrestling with God was a forceful man. Joseph imprisoning Simeon was a forceful man. The patriarchs selling Joseph as a slave were forceful men. Samson slaying the Philistines was a forceful man. David slaying Goliath was a forceful man.
Any genuine Christian will be involved in spiritual warfare and will have to press their way into the kingdom.
