Our Hearts are Filled with a Thick Forest of Thorns

Mark 4:18–19, And others are the ones on whom seed was sown among the thorns; these are the ones who have heard the word, but the worries of the world, and the deceitfulness of riches, and the desires for other things enter in and choke the word, and it becomes unfruitful.

John Calvin:
Each of us ought to endeavor to tear the thorns out of his   heart, if we do not choose that the word of God should be choked; for   there is not one of us whose heart is not filled with a vast quantity,   and, as I may say, a thick forest, of thorns. And, indeed, we perceive   how few there are that reach maturity; for there is scarcely one   individual out of ten that labors, I do not say to root out, but even   to cut down the thorns. Nay more, the very number of the thorns, which   is so prodigious that it ought to shake off our sloth, is the reason   why most people give themselves no trouble about them.