There was a good discussion led by Michael Barber about the Restoration of the Kingdom and Fishers of Men over at Singing in the Reign over the symbolism of “fish” in the Old and New Covenants.
Michael reminds us that the idea of “fishers of men” was not something new with Christ’s appointment of the Apostles but something prophesied by Jeremiah 16:14-16, which ends with the words:
“Behold, I am sending for many fishers, says the Lord, and they shall catch them” (Jer 16:16).
Ezekiel also uses this image as an image of redemption from exile. Ezekiel describes a river flowing from the eschatological Temple into the sea.
Fishermen will stand beside the sea; from En-gedi to En-eglaim it will be a place for the spreading of nets; its fish will be of very many kinds, like the fish of the Great Sea. (Ezek 49:10)
Christ assigns the task of evangelistic “fishing” to the Apostles. In continuity of this tradition, St. John mentions the miraculous catch of the 153 fish after Christ has risen from the dead.
So Simon Peter went aboard and hauled the net ashore, full of large fish, a hundred and fifty-three of them; and although there were so many, the net was not torn. (Jn 21:11)
Why did St. John record the exact number? St. Augustine rightly observed its significance. 153 is the triangular of 17. That means that if you add all the numbers decreasing from 17, you get 153. That is to say, 17 + 16 + 15 + 14 +13 + 12 + 10 + … + 1 = 153.
What is the significance of the number 17? The number was a sign. St. John has a special love for the number 17. The 12 extra baskets of bread from the five barley loaves adds up to 17. (St. Augustine said that it represented the gifts of the Old and New Covenant – the Ten Commandments and the Sevenfold Spirit.)
Seventeen is also the age at which Joseph was sold into Egyptian slavery (Gen 37:2) and the Patriarch lived in Egypt for seventeen years (Gen 47:28). The Book of Acts lists seventeen nations present for Pentecost (Acts 2:7-11). Seventeen seems to be number of the nations, just as seventy also serves as the number of the nations (cf. Gen 10).
10 + 7 = 17
Peter’s catch of 153 seems to indicate the superabundance of the ingathering of the nations. A sort of “wink wink” for the reader who is in the know.
153 also is a “magic number.” Not only is it the triangular of 17, the Pythagoreans believed the number to be unique. 153 is the sum of the cubes of its own digits (1x1x1 + 5x5x5 + 3x3x3 = 153).