"Among these [apostles] Peter alone almost everywhere deserved to represent the whole Church. Because of that representation of the Church, which only he bore, he deserved to hear ‘I will give to you the keys of the kingdom of heaven’" (Sermons295:2 [A.D. 411]).
"Some things are said which seem to relate especially to the apostle Peter, and yet are not clear in their meaning unless referred to the Church, which he is acknowledged to have represented in a figure on account of the primacy which he bore among the disciples. Such is ‘I will give unto you the keys of the kingdom of heaven,’ and other similar passages. In the same way, Judas represents those Jews who were Christ’s enemies" (Commentary on Psalm 108 1 [A.D. 415]).
"Who is ignorant that the first of the apostles is the most blessed Peter?" (Commentary on John 56:1 [A.D. 416]).