The author undertakes a systematic analysis of all the passages of St. Augustine's «Tractates on the First Epistle of John» (In Epistulam Iohannis ad Parthos tractatus), in which the exegesis is influenced by the anti-Donatist polemics. The study demonstrates a complex of elaborate exegetical procedures which allowed St. Augustine to adjust the teaching of the Epistle to the «atmosphere of hatred and violence» still reigning in Hippo about 407. Only in two cases (Tr. 1, § 8 and 2, § 4) Augustine's anti-Donatist speculation on the text may be said to be hardly rooted in its original sense, but rather to use the text as a starting point. Elsewhere, the obvious meaning is modified in various ways. The meaning of «scandal» (or «cause for stumbling») and «walking in darkness» is specified as «being scandalised about the Church» (or «hitting oneself against the Church») and «incapability to see the Church» (Tr. 1, § 12 and 2, § 4 on 1 John 2:10-11) respectively. John's warnings against false doctrine are redirected against the schism, the sense of false doctrine being thus enlarged in a way to include not only misleading words about Christ, but also mischievous works against his Church (Tr. 3, § 4-5, 7-8 and 6, § 11-14 on 1 John 2:18-19, 21-22 and 4:1-3). John calls for charity and self-denial as manifestations of love, but Augustine points out that the most obvious manifestation of true love for one's brothers is keeping peace within the Church; therefore, if the unity and peace are violated, there is no love, and works of mercy and acts of self-denial, being manifestations not of love, but of something else (e.g. of vain glory), are not valid. In this way John's call for compassion and selflessness is developed and supplemented to become a demand for unity (Tr. 6, § 2 on 1 John 3:16-18). Finally, commenting on John's words that love for God is seen in keeping his commandments, Augustine reminds that the essence of these commandments consists in brotherly love (implying the unity of the Church, which the Donatists violate). The procedure used here may be regarded as a concentration of the original meaning (Tr. 10, § 8-10 on 1 John 5:1-3). The «Tractates...», even considered in one aspect, that of anti-Donatist interpretation, show Augustine at his best not only as a champion of caritas and unitas, but also as a mature master of homiletic exegesis.