Proclaim the one truth, and whoever is of the truth will hear you (cf. Jn 18:37). Such is the content of the present apostolic lesson. Who these teachers of other doctrine are, the Apostle does not define particularly. He speaks generally: they teach otherwise and do not consent to the sound words of the Lord and to the doctrine according to piety.
Here one may understand all Christian teaching, both dogmas and rules of life and sanctification through the Mysteries. Whoever departs in anything from the words of the Lord and from the sound doctrine held by the assembly of the pious is a teacher of other doctrine. He is a proud disputant over words, unworthy of communion.
Therefore "these things teach and exhort" (1 Tim 6:2) refers not only to the submission of slaves, but to everything set forth above, without excluding that submission.
The sound words of the Lord are those about which He testified: "All that I have heard from My Father I have made known to you" (cf. Jn 15:15). They are the same as what the Holy Spirit suggested to the Apostles. For He too was to speak whatever He heard (Jn 16:13). Of course, whatever He spoke, He spoke as He heard.
The sound words of the Lord therefore contain the truth hidden in the mystery of the Tri-hypostatic God, brought to earth by the incarnate Son of God, and spread among men through the Apostles by the Holy Spirit. It is sound truth, that is, pure, unmixed, and unalterable.
They are sound because they contain pure truth and because they give health to the soul that receives them. Truth brings health to the soul, while falsehood, even a small falsehood, weakens it and makes it infirm.
The doctrine according to piety is composed of the sound words of the Lord and the revelations of the Holy Spirit. It gathers all the words into one and from all the truths announced by them forms a single whole. It forms one image of contemplation of the work of salvation in the Lord Jesus Christ, by the grace of the Holy Spirit, according to the good pleasure of the Father.
The Lord said many things, and the Apostles also said many things by the Holy Spirit. Those who heard and received them laid all things up in their hearts. The heart, like a certain architect, guided by grace, ordered this image of contemplation of the work of salvation. This image contained the doctrine according to piety.
Established under the influence of the Apostles, this image was carried in the hearts of believers out of the apostolic age. It was renewed and preserved by their successors and handed down to the following generations of the faithful. From them, by mutual succession, it has come down to us.
Thus the doctrine according to piety is the doctrine held by the Church, then under the Apostles and now by succession from them.
In Greek it does not say "right faith," but "piety," τη κατ ευσεβειαν διδασκαλια. This is not a departure from the Apostle's original word, but its most exact expression. Piety is the heart's relation to God. Life according to piety is life in the fear of God, for the glory of His all-holy name. Doctrine according to piety is doctrine held through undoubting faith in the word of the God of truth. Such holding of the truth is truly right faith, and it alone is such.