By St. Maximus the Confessor
"Simon Peter went up and drew the net to the land, full of large fish, a hundred and fifty-three; and though there were so many, the net was not torn" [Jn. 21:11].
What does the number of the one hundred and fifty-three fish in the Gospel signify?
By beginning at one and adding until seventeen [1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 + 11 + 12 + 13 + 14 + 15 + 16 + 17 = 153], you will generate this number. Thus, this signifies that precisely through the fulfillment of the ten commandments and through the seven activities of the Holy Spirit, those who are being saved will enter into the kingdom of the heavens; or also, it signifies those who are being saved and made worthy of the kingdom through the Faith of the Holy Trinity and by the hope of things to come - for the number fifty goes beyond the sevenfold [number] of weekly time - and by the operation of the commandments, which is signified by the number one hundred.
From Questions and Doubts, "Question 56," trans. Despina D. Prassas (DeKalb, IL: Northern Illinois University Press, 2009), p. 74.