John Gill Commentary Mark 4:17

"and they have no root in themselves, but endure for a while; then, when tribulation or persecution ariseth because of the word, straightway they stumble." — Mark 4:17 (ASV)

And have no root in themselves
The word has no root in their hearts, only in their natural affections: nor is the root of grace in them; there is no heart work, only speculative notions, and flashy affections:

and so endure but for a time :
they continue hearers and professors of the Gospel but for a small season; like the Jews, who rejoiced in the ministry of John the Baptist for a while, and then left him:

afterward, when affliction or persecution arises for the word's
sake, immediately they are offended .
As soon as any small degree of trouble comes upon them, and especially when there is a hot persecution of the professors of religion, because of the Gospel they have embraced; such hearers are stumbled at these things, and cannot bear the loss of any thing, or endure any thing severe for the sake of the word they have professed a pleasure in; and therefore, rather than suffer, they relinquish at once their profession of it.