Extra-Scriptural teaching is rejectable as human — Scripture the examination rule
Church teachers' delivery can be rejected as human tradition only because it stands outside Scripture.
If God's word were not bounded by Scripture and an unwritten divine word also existed, teachers could rightly claim their teaching is that word — and if we needed an unwritten word, where else would we take it?
Yet Christ shows Church doctors can propose mere human invention as God's word.
Therefore whatever can be proposed outside Scripture's substance counts as human doctrine, and Scripture is the rule for examining all things — otherwise magisterial precepts could never be rejected as human traditions.
Latin
XXVIII. Denique quod tradunt & docent Ecclesiae Doctores non potest rejici tanquam humana traditio, nisi quia est extra Scripturam. Etenim, si Dei verbum Scriptura sacra determinatum non esset, sed praeterea extaret verbum Dei non scriptum, jure possent obtendere Ecclesiae Doctores sua documenta esse illud ipsum Dei verbum. Et revera, si ad aliquod verbum Dei non scriptum nobis recurrendum esset, unde potius deberet accipi quam ab ipsis? Cum ergo nihilominus contingat, teste Christo, Ecclesiae Doctores pro Dei verbo proponere quod non est aliud quam humanum commentum; inde manifestum est habendum esse pro doctrina hominum, quicquid extra Scripturae substantiam proponi potest, & Scripturam regulam esse ad quam omnia examinanda sunt: alioquin, ut diximus, Magistrorum Ecclesiae praecepta & documenta, tanquam traditiones humanae, rejici non possent.