Jamieson, Fausset and Brown on Mark 4:15

15. And these are they by the wayside, where the word is sown; but, when they have heard, &c.--or, more fully (Mt 13:19), "When any one heareth the word of the kingdom, and understandeth it not, then cometh the wicked one, and catcheth away that which was sown in his heart." The great truth here taught is, that hearts all unbroken and hard are no fit soil for saving truth. They apprehend it not (Mt 13:19) as God's means of restoring them to Himself; it penetrates not, makes no impression, but lies loosely on the surface of the heart, till the wicked one--afraid of losing a victim by his "believing to salvation" (Lu 8:12)--finds some frivolous subject by whose greater attractions to draw off the attention, and straightway it is gone. Of how many hearers of the word is this the graphic but painful history!