Karma is a concept found in many eastern religions that essentially says, “What goes around, comes around.” It is a sort of universal law of cause and effect.
However, in looking at the text preceding it, we see that the premise behind this concept is not a universal law, but rather a just God who will not let the unjust forever get off scot-free or the righteous not eventually be rewarded.
In the Amplified version expands on this nicely, allowing the fuller impact of the original language to be felt:
“Do not be deceived and deluded and misled; God will not allow Himself to be sneered at (scorned, disdained, or mocked by mere pretensions or professions, or by His precepts being set aside.) [He inevitably deludes himself who attempts to delude God.] For whatever a man sows, that and that only is what he will reap.” [Galatians 6:7]
So what at first glance appeared to be a restatement of karma is really the reflection of the character of a God who is fair and just.