In this group of three parables, which have a positive content, the first parable, of the treasure in the field, was about Israel. The parable of the pearl is about the ecclesia (>church).
45 Again, the kingdom of heaven is like a man, a merchant, seeking excellent pearls.
46 And when he finds one pearl of great price, he goes and sells all that he had and buys it.
a man
This man, as we now know, is the Son of Man (:37). He gave everything He had to buy that one pearl. We could relate that to the incarnation of the Lord. He came to give His life and die, to then rise again and so He bought us (1 Cor. 6:20).
In the Greek it literally says: going away, he has dealt with everything and this has the grammatical form of a situation that began in the past and continues in the present.
The Lord has not only done a work in the past, but He is also doing a work for us now: He gives Himself completely for the ecclesia. He sanctifies her, cleanses her in His word and she is without spot or wrinkle (Eph. 5:25-27).
pearls
There is not much about pearls in the Bible. They appear in lists where wealth is described (Rev. 17:4; 18:12), as a description of the new Jerusalem (Rev. 21:21), where many other precious stones are also mentioned and as an adornment for women (1 Tim. 2:9).
It is remarkable that pearls are associated with dogs and pigs (Matt. 7:6), in the Bible they are both a representation of the nations. It is remarkable that pearls are mainly formed in oysters and are dredged up from the sea, which we saw earlier is also a representation of the nations.
suffering
Pearls are formed when something (for example a grain of sand) enters the shell and the oyster treats this foreign part as an intruder to protect itself. As a result, the oyster forms mother-of-pearl around the intruder.
The pearl is formed through a process of suffering. The ecclesia is also said several times to be formed through suffering (2 Cor. 1:5; Phil. 3:10; Col. 1:24).
A pearl is formed in secret, just as the ecclesia is (Col. 1:27), but a pearl is meant to come out of the secret and when revealed, it is a precious and honorable stone, a jewel and a representation of glory.
Romans 8
18 For I reckon that the sufferings of this present time are not worthy to be compared with the glory which shall be revealed in us.
shape
A pearl is round and that is an image of imperishability. As we still know from wedding rings, which symbolize an everlasting bond.
An oyster is a shell that consists of two parts. The pearl is formed between them. This is also the case with the ecclesia, it is formed between the coming and return of the Lord, in the interruption.
colour
A pearl is white. That speaks of purity and glory. The ecclesia is said to be: glorious, holy and spotless (Eph. 5:27). White is not actually a color, but a composition of the different colors. God now makes His multi-colored wisdom known through the ecclesia.
Ephesians 3
10 so that now through the ecclesia, to the rulers and authorities in heaven, the manifold wisdom of God might be made known.
one
A pearl is indivisible. Diamonds can be cut, but a pearl cannot. A pearl is a unity, just like the ecclesia, the body of Christ. It has many members, but is one body (1 Cor. 12:12).
In this parable too, we no longer see what happens to the pearl. That remains hidden, because the parables speak about the period when the Kingdom is hidden.