30 But the Lord prayed and besought not for Himself— for why should He who was guiltless pray on His own behalf?— but for our sins, as He Himself declared, when He said to Peter, “Behold, Satan has desired that he might sift you as wheat. But I have prayed for you, that your faith fail not.” And subsequently He beseeches the Father for all, saying, “Neither pray I for these alone, but for them also which shall believe in me through their word; that they all may be one; as You, Father, art in me, and I in You, that they also may be one in us.” The Lord's loving-kindness, no less than His mercy, is great in respect of our salvation, in that, not content to redeem us with His blood, He in addition also prayed for us. Behold now what was the desire of His petition, that like as the Father and Son are one, so also we should abide in absolute unity; so that from this it may be understood how greatly he sins who divides unity and peace, since for this same thing even the Lord besought, desirous doubtless that His people should thus be saved and live in peace, since He knew that discord cannot come into the kingdom of God.
Source: The Treatises of Cyprian (New Advent)