The Gospel of John and particularly the first chapter demonstrates the Divinity of Jesus. This Gospel in itself is the greatest support of Athanasius's stand. The Gospel of John's first chapter began to be said at the end of Mass, we believe as a result of Athanasius, and his life's stand, but quietly. The Last Gospel of The Mass, The Eucharist, St John[1:1–14], together with the prayer; "Placeat tibi", the Blessing, are all private devotions that have been gradually absorbed by the liturgical service. The beginning of John's Gospel was much used as an object of special devotion throughout the Middle Ages. Nevertheless, the practice of saying it at the altar grew; eventually Pius V made this practice universal for the Roman Rite in his edition of the Missal (1570). It became a firm custom with exceptions in using an other Gospel in use from 1920. So the Missals showed different last Gospel for certain Feast days. A Prayer Card for the St John's Gospel. Also:
Why is the Gospel of John said at the end of Catholic Mass?
a result of Athanasius