“They said therefore among themselves, Let us not rend it, but cast lots for it, whose it shall be: that the scripture might be fulfilled, which saith, They parted my raiment among them, and for my vesture they did cast lots. These things therefore the soldiers did.”
So they said to each other, 'Let us not tear it, but cast lots for it.' This was to fulfill the scripture that says, 'They divided my clothes among them, and for my clothing they cast lots.' — The soldiers' decision not to tear but to gamble for the tunic (lots cast on the seamless robe) follows Psalm 22:18 precisely. John's fulfillment formula (hina plērōthē to rēma) indicates that Jesus' passion fulfills Scripture, not randomly but according to divine design. The crucifixion's details—from inscription to garments—manifest God's preordained word.
Church Fathers on John 19:24
The Evangelist describes the tunic, to show that it was of an inferior kind, the tunics commonly worn in Palestine being made of two pieces.
Others say that they did not weave in Palestine, as we do, the shuttle being driven upwards through the warp; so that among them the woof was not carried upwards but downwards.
They said therefore among themselves, Let us not rend it, but cast lots for it whose it should be. It seems then that the other garments were made up of equal parts, as it was not necessary to rend them; the tunic only having to be rent in order to give each an equal share of it; to avoid which they preferred casting lots for it, and one having it all. This answered to the prophecy: That the Scripture might be fulfilled which says, They parted My raiment among them, and for…