ISB ~ 2 Thessalonians 2 v15

the traditions:The teaching that Paul handed over to his readers, whether in writing or by oral instruction. This was the standard against which doctrinal claims (2:5) and moral behavior (3:6) were to be measured and judged. Even Paul’s personal example was a form of apostolic catechesis (3:79; 1 Cor 11:2; 2 Tim 1:13) (CCC 75-76, 82).

• The apostles did not hand down everything in writing; many unwritten things were handed down as well, and both written and unwritten are worthy of belief. So let us also regard the tradition of the Church as worthy of belief (St. John Chrysostom, Homilies on 2 Thessalonians 4).