Our reflection for the 21st Sunday through the Year on Matthew 16:13-20 comes from St. Cyril of Alexandria:
“Peter did not say ‘you are a Christ’ or ‘a son of God’ but ‘the Christ, the Son of God.’ For there are many christs by grace, who have attained the rank of adopted sons, but only one who is by nature the Son of God. Thus, using the definite article, he said, ‘the Christ, the Son of God’. And in calling him the Son of the living God, Peter indicates that Christ himself is life and that death has no authority over him. And even if the flesh, for a short while, was weak and died, nevertheless it rose again, since the Word, who indwelled it, could not be held under the bonds of death.”