“Do those things that prove that you have turned to God and have changed the way you think and act. Don’t say, ‘Abraham is our ancestor.’ I guarantee that God can raise up descendants for Abraham from these stones.
9 The ax is now ready to cut the roots of the trees. Any tree that doesn’t produce good fruit will be cut down and thrown into a fire.”
10 The crowds asked him, “What should we do?”
11 He answered them, “Whoever has two shirts should share with the person who doesn’t have any. Whoever has food should share it too.”
12 Some tax collectors came to be baptized. They asked him, “Teacher, what should we do?”
13 He told them, “Don’t collect more money than you are ordered to collect.”
14 Some soldiers asked him, “And what should we do?”
He told them, “Be satisfied with your pay, and never use threats or blackmail to get money from anyone.”
If you were to read starting from verse 10, it would just look like commands of what people need to do to please God and be one of his children, as opposed to the fact that they are descendants of Abraham being the only thing necessary.
Although James seems to make is clear in what he’s explaining regarding good works–writing that it’s the kind of faith that saves us (James 2:14), how good works show that our faith is genuine (James 2:22), James and John the Baptist using the word or metaphor of deadness (Luke 3:8-9, James 2:26 [stones, bad or dead fruit]) etc., some still seem to have a hard time with this. So we can go to other parts of the Bible like Luke, which happens to be written after James (did Luke know what James wrote?) to find more explanatory material. Luke explains that these good works are proof (as in God’s Word Translation, NET and NLT to name a few) while most say, Bear fruits in keeping with repentance as does ESV, NASB and NIV. If it wasn’t for the former, I’m not sure I would understand the latter, looking at that part of that verse by itself.
Joel B. Green, in his commentary on Luke, makes some very interesting (to me anyway) parallels on the current (in the narrative) descendants of Abraham who feel their pedigree is enough, to some of what’s written in the Old Testament. Since Luke’s narrative here is describing John the Baptist speaking to a specific nationality and religion, he can utilize their own heritage and knowledge to convict them of their prideful and incorrect view of their standing before God.
Such an understanding is repudiated by John, who insists that children of Abraham are not identified by birth into the covenant community but through response to God’s gracious initiative. The crowds are like the wilderness to which they have come to hear John — empty, unproductive, lifeless — and so they must become fruitful, producing in their lives behaviors that demonstrate their relation to God (cf. Acts 26:20).
John produces two warnings to the crowd, both of which follow hard upon his declaration that their privileged status is now insecure. First, he reminds them that they can be replaced by stones! John draws on a number of pertinent images — Abraham, the father of many nations; the ability of God to give Abraham a child (Genesis 18:14); the portrayal of “stones” as inanimate, used as a metaphor for lifeless gods and humans (cf. Acts 17:29); the election and shaping of a nation, God’s people, in the exodus and crossing of the Jordan, together with the stones to memorialize the event; the fact that God’s promises to Abraham have been coming to realization in the Lukan narrative (Luke 1:55, 73)…
As in the Scriptures, the behaviors for which John calls are not themselves the basis for membership in God’s covenant people; rather, they are manifistations of that relatioinship. To put it differently, these are the natural outgrowth of lives reoriented around the God who is himself merciful (cf. Luke 6:36).
Joel B. Green, The Gospel of Luke, pgs. 176; 178
Many other things could be written about like the Beatitudes, what Jesus Himself said about these things etc.