The answer is actually found here -

"Luke 16:16
"The Law and the Prophets were proclaimed until John. Since that time, the good news of the kingdom of God is being preached, and everyone is forcing their way into it.


What Dr Walter martin used to say about this very same question is that we can take the idea of a bunch of sheep that have been locked up in a pen all night.
Then the owner of the sheep goes to the pen and he pulls away a few of the boards, just enough to allow one sheep at a time to get out....except that Sheep are not good at the whole "one at a time" thing.
So the moment the sheep see the small opening they all try to get out at the same time....(sheep hate to be the last one)

The image here is the same as in the verses we are talking about.
Where the sheep are forcing their way though the small gate....rushing to hear the Good News!