Steve Runge of Logos Bible Software uses Galatians 3:7 as an example to show “how discourse considerations can inform text-critical judgments.”
The two options available to textual critics are:
NA27: γινώσκετε ἄρα ὅτι οἱ ἐκ πίστεως, οὗτοι υἱοί εἰσιν Ἀβραάμ.
Alternate: γινώσκετε ἄρα ὅτι οἱ ἐκ πίστεως, οὗτοι εἰσιν υἱοί Ἀβραάμ.
I’ll let you surf over to read his reasoning but here is his conclusion:
If anything, it provides more support for the NA27 reading since it is the dis-preferred reading, the one more likely to have been corrected by a later hand (as appears to be the case from Sinaiticus). However it illustrates what is at stake in such decisions. It is not just a matter of one little word inconsequentially being swapped with another. Such changes can radically alter our understanding of where Paul was pounding the pulpit.
Stephen Carlson has also weighed in on the issue.
Paul's Epistle to the Galatians 