For example, in Mark 10:18 Mark says:
"Why do you call me good?" Jesus asked him. "No one is good except God alone." (CSB)
But in Matthew 19:17:
"Why do you ask me about what is good?" Jesus replied. "There is only One who is good. If you want to enter life, keep the commandments." (NIV)
What’s happening here? Why is Matthew changing the text and making it less harsh?
Can someone explain?
I find this phenomenon fascinating—so much so that I once made a couple videos about it. The phenomenon is discussed here, and my conclusions from it here.
Discerning the relationship among the Synoptic Gospels (Matthew, Mark, Luke) is known as the Synoptic Problem—at the bottom of the post I’ve shared links to several of the major views, as discussed on this site.
The traditional explanation
Markan Priority—the view that Mark was the first of the Synoptic Gospels written, has held a dominant position in New Testament scholarship since the 1870s in German and the 1920s in English. Most who believe in Markan Priority believe that Matthew & Luke each later used Mark as a source. One of the key data points used to argue that Mark was first is what is known as Mark’s “hard sayings”.
Mark’s Greek is often more awkward than that of Matthew & Luke, including errors of grammar, consistency, and unusual word-choice. Mark also includes statements that tend to cast Jesus (or others) in a more negative light—such as the passage in the OP, the insinuation that Jesus was “beside Himself” (Mark 3:21) or that Jesus “could there do no mighty work” in His own country (Mark 6:5).
Those arguing for Markan Priority have suggested that it was only natural that Matthew & Luke would, in drawing material from Mark, smooth out the rough patches—to include fixing bad grammar and improving upon awkward or unflattering statements.
The evidence
The Synoptic Problem has not been solved to general satisfaction, and it remains a point of debate in New Testament scholarship. The early Christian historians were unanimous in testimony that Matthew was written first (see Frank Luke’s summary of the patristic testimony here and my summary here).
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The idea that later writers always improve/polish the material of sources they quote sounds intuitive and appealing, but it is not anything close to consistently true. There are numerous 2nd+ century Gospels that quote the canonical Gospels, and the later non-canonical Gospels degrade the grammar of their sources.
An interesting challenge is this: among the numerous non-canonical Gospels, find one that is as much a well-crafted masterpiece as the 4 canonical Gospels. The canonical Gospels are without peer (Note that Mark is a masterpiece--but the genius of Mark isn't grammar, it's the storytelling--see more below).
William Farmer summed this up well:
Since sometimes writers improve the grammar of their sources while others spoil it, such considerations provide no objective basis by which one document may be adjudged primary or secondary to another. There is no provable correlation between style and chronology (see here)
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That Mark’s Gospel comes across a little different than that of Matthew or Luke has been known and studied for more than 1900 years. Two Christian historians, Papias of Hieropolis & Clement of Alexandria provided testimony as to why this is.
Both Papias (~105) & Clement (~200) recorded that the Gospel of Mark was based on preaching by Peter. Since Clement provides a number of details not found in any known fragment of Papias (and since Clement was from the Alexandrian church Mark is said to have founded), it is likely that Clement has at least some independent information (For the testimony of Papias, see HE 3.39; for several of the key statements by Clement see HE 2.15 & HE 6.14).
This means we have at least 2 early sources for a very significant claim about Mark’s origin:
The material came from Peter
The material was based on preaching
Putting the pieces together
If Mark is the long-hand version of short-hand sermon notes, many of the features of Mark make a lot more sense:
I am of the view that the hard sayings of Mark are best explained by Mark’s origin in oral preaching, not Markan Priority, and that Matthew was indeed first—but it is more polished because it was designed as a literary treatise, not given as a sermon like the material found in Mark. This would not only be consistent with the independent, early testimony of Papias & Clement, but also with the unanimous patristic testimony in favor of Matthean Priority.
Conclusion
Matthew softens "Mark’s sayings" in that Matthew was designed to convey the ministry of Jesus in writing, whereas Mark preserves the ministry of Jesus as it was preached by Peter. Matthew need not be editing the text of Mark at all.
Appendix
Several posts on this site that review the question of priority (who was first) in the Synoptic Problem:
What are the arguments in favor of Matthean Priority?
What are the arguments in favor of Markan priority?
What are the arguments in favor of Lukan Priority?
Why is Matthew changing the text and making it less harsh?
Allow me to quote from the NAS:
Mark 10:17-18: As He was setting out on a journey, a man ran up to Him and knelt before Him, and asked Him, “Good Teacher, what shall I do to inherit eternal life?” And Jesus said to him, “Why do you call Me good? No one is good except God alone.
Matthew 19:16-17a: And someone came to Him and said, “Teacher, what good thing shall I do that I may obtain eternal life?” And He said to him, “Why are you asking Me about what is good? There is only One who is good..."
As you have noted, the texts vary slightly. In Mark, this man came to Christ and began his question with: "Good Teacher, what shall I do..." This is different from Matthew's account, in which the same man is quoted as merely saying "Teacher, what good thing shall I do" -- without addressing Christ as "good."
In both instances, Jesus is answering questions based on how we are told they were asked. In Mark, the Lord addresses the designation the man uses for Him first. Christ then responds to the second clause of that same question. Some would immediately characterize this as a biblical contradiction between Mark and Matthew, but I propose that such is unfounded.
Often, when we read Scripture, we are not privy to full conversations. I suggest there are many instances, like this one, where we receive pieces of a greater whole. It is only when the full text is essential that the record of a complete conversation is conveyed to us.
As may be the case here, the inspired writers faithfully relate only selected information for the greater message of the narrative, as well as the perspective of that particular writer. The full address by the rich young ruler may well have been:
"Good Teacher, what good thing shall I do, that I may inherit eternal life?"
If true, the young man seems to be using the word "good" a bit gratuitously, perhaps resulting in an altered response. (Obviously, this is just an educated guess.)
