Luke 13:24 Strive to enter in at the strait gate: for many, I say unto you, will seek to enter in, and shall not be able.
This is a very unusual statement. Why is it unusual? Because the strait gate is the correct gate. It is the narrow way that leads to life. And typically the "many" do not seek to enter into that gate.
The many typically desire to go the broad way:
Matthew 7:13 Enter ye in at the strait gate: for wide is the gate, and broad is the way, that leadeth to destruction, and many there be which go in thereat:
Since many normally go the way of the broad gate, we can see why Luke 13:24's statement regarding 'many' seeking to enter the strait gate is indeed unusual. The strait gate would be the proper way of entering into heaven. It would be the way of Christ by His grace and by His faith.
We know this because anything else would be part of the broad way that leads to destruction.
So, it appears that God is saying that once the door of heaven is shut, there will be large numbers of people on the earth who will then, finally, begin to seek Him in the proper way.
However, the tragic part is that although they will finally seek to enter into heaven the right way, nonetheless, they will not be able to enter in. The door has been shut:
Luke 13:24 Strive to enter in at the strait gate: for many, I say unto you, will seek to enter in, and shall not be able.
25 When once the master of the house is risen up, and hath shut to the door, and ye begin to stand without, and to knock at the door, saying, Lord, Lord, open unto us; and he shall answer and say unto you, I know you not whence ye are: