The dissertation investigates the issue of the strong and the weak in faith from Rom 14,1 – 15,13 in the context of Paul's theology of justification by faith and in relation to the issue of the strong and the weak in conscience from 1 Cor 8,1 – 11,1 through a synchronic and diachronic approach of the historical-critical method. The investigation of the issue was limited to seven authentic epistles of Paul. The exegetical analysis of the unit Rom 14,1 – 15,13 pointed to four specific elements from which we learn that the issue of the strong and the weak in faith is motivated by the conflict between Jewish Christians and Gentile Christians regarding the observance of Jewish holidays and dietary regulations, which is why Paul calls them to mutual acceptance that would create union in community. Also, Paul places their conflict and his paraenetical encouragement in the context of faith. In addition, the analysis of the unit showed that the Apostle gives seven reasons for the unity of Roman Christians, which are connected with the doctrinal part of the Epistle where the theology of justification by faith is presented. The research results show that the connection is at the semantic and theological levels. The issue of the unity of the strong and the weak in faith in the entire context of the Epistle is reflected in the Apostle's effort to interpret universal salvation, which includes Jews and Gentiles. Because of all the above, it was concluded that unit 14,1 – 15,13 is crucial for the understanding of the Epistle to the Romans and that the Apostle's teaching on justification by faith concerns the specific problems of Roman Christians. This unit is crucial because through it we can see the true understanding of the content of the Epistle, the subject of which is life according to the gospel, while justification by faith is its fundamental presupposition. Thus, the theology of justification by faith is not presented as doctrine per se but serves the Apostle to achieve ecclesial-pastoral undertakings. In the last phase of the analysis, the conclusion was reached that the problem of the Roman Christians in terms of the strong and the weak in faith is not identical to the problem of the Corinthian Christians, which is why Paul approaches the solution of the mentioned problem in a unique way. Namely, in 1 Cor he does not use the theology of justification by faith as a basis for the mutual acceptance of the community.