John Chrysostom

"But thou hast fully known my doctrine." Wherefore be strong; for thou wert not merely present, but didst follow closely. Here he seems to imply that the period had been long, in that he says, "Thou hast followed up my doctrine"; this refers to his discourse. "Manner of life"; this to his conduct. "Purpose"; this to his zeal, and the firmness of his soul. I did not say these things, he says, and not do them; nor was I a philosopher in words only. "Faith, longsuffering." He means, how none of these things troubled me. …

Homily on 2 Timothy 8 ↗

Theophylact of Ohrid

Those, he says, are such, but you know well our relationship, and it is not like that: you did not simply attach yourself to me, but also "followed," that is, spending a long time and sharing everything with me, you attended to all that was mine and became practiced in it. Be then steadfast and fight against the adversaries. "In teaching," that is, in the word. That is, in life and morals. That is, in zeal and manly enthusiasm. For I, he says, not only taught, but also practiced. …

Commentary on 2 Timothy ↗

Oecumenius

But you followed my teaching, my conduct, my purpose, my faith, my patience, my love, my endurance, my persecutions, my sufferings, such as happened to me at Antioch, at Iconium, and at Lystra, what persecutions I endured; and out of them all the Lord rescued me. Indeed, those are such, Paul said, but you know that mine are not of this kind. For you did not simply accompany me, but you followed closely, that is, you accompanied me for a long time, and you paid attention to all my teachings. …

Commentary On 2 Timothy ↗

Thomas Aquinas

Then when he says, but you have fully known my doctrine, he shows that Timothy is ready to resist in the face of such dangers: first, he shows that he was fit to be appointed an apostle; second, from his familiarity with the Scriptures, at because from your infancy (2 Tim 3:15). In regard to the first he does two things: first, he shows that he was carefully instructed by the Apostle; second, how he could be instructed by others, at all that will live godly in Christ shall suffer persecution. …

Commentary on 2 Timothy ↗