It's important to see the last verses of this Passage in Matthew 7 as the end of a Herod story, a story about the construction of Caesarea as a Safe Harbor that allows grain from Petronius, Procurator of Egypt to be unloaded and distributed to the people of Judea. The Priestly Groups fear that this "Kindness" will be for the glory of Herod and not for the Glory of God, as reflected in Mark 9: 42, quoted above.
 "Enter by the narrow gate; for the gate is wide and the way is easy, that leads to destruction, and those who enter by it are many.
 For the gate is narrow and the way is hard, that leads to life, and those who find it are few.
, 15, 9, 6:
"This city is situate in Phoenicia, in the passage by sea to Egypt, between Joppa and Dora, which are lesser maritime cities, and not fit for havens, on account of the impetuous south winds that beat upon them
, which rolling the sands that come from the sea against the shores, do not admit of ships lying in their station; but the merchants are generally there forced to ride at their anchors in the sea itself
Thus the problem. It is a treacherous stretch and the ships cannot even approach the shoreline without fear.
Definition: "Mole": A massive work formed of masonry and large stones or earth laid in the sea as a pier or breakwater
Herod begins construction of a Safe Harbor:
"...and this he effected by letting down vast stones of above fifty feet in length, not less than eighteen in breadth, and nine in depth, into twenty fathom deep; and as some were lesser, so were others bigger than those dimensions. This mole which he built by the sea-side was two hundred feet wide, the half of which was opposed to the current of the waves, so as to keep off those waves which were to break upon them, and so was called Procymatia, or the first breaker of the waves
; but the other half had upon it a wall, with several towers, the largest of which was named Drusus, and was a work of very great excellence, and had its name from Drusus, the son-in-law of Caesar, who died young. There were also a great number of arches where the mariners dwelt. There was also before them a quay, [or landing place,] which ran round the entire haven, and was a most agreeable walk to such as had a mind to that exercise; but the entrance or mouth of the port was made on the north quarter, on which side was the stillest of the winds of all in this place
: and the basis of the whole circuit on the left hand, as you enter the port, supported a round turret, which was made very strong, in order to resist the greatest waves..."
For the gate is narrow and the way is hard, that leads to life, and those who find it are few
PS: This Passage is radically different from the Story of "Enter through the Narrow Door", found in Matthew 18: 2 - 4 and Luke 13: 23 - 24. These two Fragments tell of the Saving of the Priest and have nothing to do with the Construction of Caesarea.