John Wesley on John 17:12

Those whom thou hast given me I have guarded, and none of them is lost, but the son of perdition - So one even of them whom God had given him is lost. So far was even that decree from being unchangeable! That the Scripture might be fulfilled - That is, whereby the Scripture was fulfilled. The son of perdition signifies one that deservedly perishes; as a son of death, 2Sam 12:5; children of hell, Mt 23:15, and children of wrath, Eph 2:3, signify persons justly obnoxious to death, hell, wrath. Psalm 109:8.