John Gill Commentary Mark 4:6

"and when the sun was risen, it was scorched; and because it had no root, it withered away." — Mark 4:6 (ASV)

But when the sun was up, it was scorched
When persecution arose because of the word, and that became very hot and vehement, it tried and pierced through this thin speculative knowledge of the word, which could not stand before it, and bear the heat of it:

and because it had no root, it withered away ;
the word had only a place in the head, and not in the heart; wherefore the profession of it was soon dropped, and came to nothing.