In this heartfelt correspondence, Pope Celestine I conveys both comfort and sorrow in light of recent challenges to the Church's teachings, particularly due to the influence of Nestorius. The letter praises Cyril of Alexandria for his unwavering commitment to the orthodox faith and his ability to effectively counter heretical views. The author emphasizes the importance of vigilance and encourages Cyril to continue his defense of the faith, while also expressing a desire to assist in the spiritual guidance of those misled by false teachings. The overarching theme is the call to protect the faith and shepherd the flock diligently.