Some texts from the bible that disprove your uncle’s claim that once saved no good works are needed.
Suggest first that he reads Matthew 25 verses 31-46 where Jesus demonstrations that His criteria for judging souls fit for heaven is whether they have lived practical acts of kindness to others,
and those who have not, go to hell, which is existence without love as they have not lived out the command to love God above all, and others as self in practical kindness.
Yes our grace and goodness comes from God, but we are judged on our practical response to these graces, our actual living-out of our Baptism, and by doing so we accept His redemption of us.
Paul also says, in Phillipians 2:12
" work out your own salvation with fear and trembling;
for God is at work in you, both to will and to work for his good pleasure.
13 It is God who, for his own generous purpose, gives you the intention and the powers to act.
14 Let your behaviour be free of murmuring and complaining
15 so that you remain faultless and pure, unspoilt children of God surrounded by a deceitful and underhand brood, shining out among them like bright stars in the world."
We must work at our salvation while receiving God’s grace, so that we remain faultless and pure, by God’s grace. If we were simply justified then we would not have to work at our salvation to ‘remain’ saved
Your Uncle may also like into account the words of James, apostle and disciple of the Lord?
Yes Jesus is our Savior and redeemer and from God comes all grace.
But James warns us:
"Take the case, my brothers of someone who has never done a single good act but claims that he has faith. Will that faith save him?
If one of the brothers or one of the sisters is in need of clothes and has not enough food to live on, and one of you says to them, ‘I wish you well; keep yourself warm and eat plenty’, without giving them these bare necessities of life, then what good is that?: if good works do not go with it, it is quite dead.
This is the way to talk to people of that kind:'You say you have faith and I have good deeds; I will prove to you that I have faith by showing you my good deeds–now you prove to me that you have faith without any good deeds to show.
You believe in one God–that is creditable enough, but the demons have the same belief, and they tremble with fear. Do realise, you senseless man, that faith without works is useless. You surely know that Abraham our Father was justified by his deed, because he offered Isaac on the altar? There you see it; faith and good deeds were working together; his faith became perfect by what he did. This is what scripture really means when it says: Abraham put his faith in God, and this was counted as making him justified; and that is why he was called the friend of God. You see now that it is by doing something good, and not only by believing, that a man is justified." [James 2: 14-24]