Actually Titus 1 & 2 gives a good discourse on sound doctrine and what becomes it.
But it doesn't
claim to be sound doctrine at all.
Whereas good doctrine s
ays that it is important.
Which is a far higher calling than a random letter.
Mark 12:31
The second is this: ‘You shall love your neighbor as yourself.’
There is no other commandment greater than these.”
James 2:8
If you really fulfill the royal law according to the Scripture, “You shall love your neighbor as yourself,” you are doing well.
Romans 15:2
Let each of us please his neighbor for his good, to build him up.
Matthew 7:12
“So whatever you wish that others would do to you, do also to them,
for this is the Law and the Prophets.
Galatians 5:14
For the whole law is fulfilled in one word: “You shall love your neighbor as yourself.”
Luke 10:27
And he answered, “You shall love the Lord your God with all your heart and with all your soul and with all your strength and with all your mind, and your neighbor as yourself.”
Romans 13:10
Love does no wrong to a neighbor; therefore
love is the fulfilling of the law.
Luke 6:31
And as you wish that others would do to you, do so to them.
Matthew 19:19
Honor your father and mother, and, You shall love your neighbor as yourself.”
Leviticus 19:16-18
You shall not go around as a slanderer among your people, and you shall not stand up against the life of your neighbor: I am the Lord. “You shall not hate your brother in your heart, but you shall reason frankly with your neighbor, lest you incur sin because of him. You shall not take vengeance or bear a grudge against the sons of your own people,
but you shall love your neighbor as yourself: I am the Lord.
Galatians 6:10
So then, as we have opportunity, let us do good to everyone, and especially to those who are of the household of faith.
Matthew 22:39
And a second is like it: You shall love your neighbor as yourself.
Luke 10:29
But he, desiring to justify himself, said to Jesus, “And who is my neighbor?”
Note, the source is not just Paul's opinion, so it is valid.