Gates" in ancient times had a significance that does not hold in the modern world. Cities then were enclosed by walls for protection; gates in the walls let people in and out to do their business, but were also the weak points in the cities' defenses. In the Bible, cities on one level represent the minds of individual people. On a broader level, they represent beliefs shared by a community. The gates, then, represent openings where the Lord can feed us an understanding of truth and a desire for good. They also represent points where the hells can invade and sway us with false ideas and evil desires. We are kept in balance during our lifetimes, with influences from both the Lord and from hell. Ideally, we will over our lifetimes continue to invite the Lord farther and farther in and drive the hells back until ultimately the Lord can occupy our minds completely. And that point our belief in Him and His power and love will hold the gates and deny evil any entrance. As individuals, we at that point become angels. As communities, we at that point become part of the Lord's church. And at that point the gates become an entry point, introductory truths that allow people to enter churches and start bringing the Lord into their lives.

916. 21:21 The twelve gates were twelve pearls: each gate was of one pearl. This symbolically means that an acknowledgment and concept of the Lord join all the concepts of truth and goodness in the Word into one and introduce into the church.

The twelve gates symbolize in sum the concepts of truth and goodness by which a person is introduced into the church (nos. 899, 900). Twelve pearls also symbolize in sum concepts of truth and goodness (no. 727). That is why the gates were pearls. Each gate was of one pearl because all the concepts of truth and goodness symbolized by the gates and by pearls relate to a single concept, one that is their containing vessel, and that single concept is a concept of the Lord. We say, a single concept, even though there are many that make up that single concept, for a concept of the Lord pervades all other doctrinal concepts, and so all concerns having to do with the church. All matters of worship take their life and soul from that concept, for the Lord is everything in the whole of heaven and the church, and so in the whole of worship.

[2] An acknowledgment and concept of the Lord join all the concepts of truth and goodness in the Word into one because all spiritual truths are connected, and if you would believe it, their connection is like the connection between all the members, viscera and organs of the human body. Consequently, as the soul holds everything together in their organization and connection, so that they are sensed only as a unit, so the Lord holds together all the spiritual truths that a person possesses.

That the Lord is the true door by which one is to enter into the church and so into heaven, He Himself teaches in John:

I am the door. If anyone enters by Me, he will be saved... (John 10:9)

And that an acknowledgement and concept of Him is the true pearl is meant by these words of the Lord in Matthew:

...the kingdom of heaven is like a merchant seeking beautiful pearls, who, when he had found one precious pearl, went and sold all that he had and bought it. (Matthew 13:45-46)

The one precious pearl is an acknowledgment and concept of the Lord.