There are many gates and walls mentioned in both the old and new testaments. Jesus spoke of a narrow gate and a wide gate, and Hells' gate. In the book of Revelation (ch 21) the description of the new Jerusalem includes 12 gates, each made of a single pearl.
If only the redeemed will inhabit the new Earth, then the gates (and walls) must be only for decoration, or perhaps for symbolic reasons. But nevertheless, they are there.
The Baptist minister, Don Piper, who wrote the book "90 Minutes in Heaven" spoke at our church a few years ago. He was declared dead at the scene of the car crash he was in, but ~90 minutes later he startled everyone when he began moving and speaking, or perhaps moaning and groaning. Anyway, I bought one of his books and when waiting for him to sign it I asked him if he saw Jesus, and he replied "No, because I never entered the gate". And then when he signed my copy of the book, he included the inscription, "I'll see you at the gate".
Perhaps there are other reasons for the gates. A certain minister I know, at the conclusion of preaching funerals, (for believers, anyway), always looks up and loudly says the name of the deceased, and then he says, "I'll meet you at the East Gate!".
