John Calvin Commentary Mark 4

That seeing, they may see, and not perceive. It is sufficient to state briefly here what has already been fully explained: that the doctrine is not, strictly speaking, or by itself, or in its own nature, but incidentally, the cause of blindness. When people with weak sight come out into sunshine, their eyes become dimmer than before, and that defect is in no way attributed to the sun, but to their eyes. Similarly, when the word of God blinds and hardens the reprobate, since this takes place through their own depravity, this effect belongs truly and naturally to them, but is incidental concerning the word.

Lest at any time they should be converted. This clause points out the advantage that is gained by seeing and understanding. It is that people, having been converted to God, are restored to his favor, and, being reconciled to him, enjoy prosperity and happiness. The true purpose for which God desires that his word should be preached is to reconcile people to himself by renewing their minds and hearts. With respect to the reprobate, on the other hand, Isaiah here declares that the stony hardness remains in them, so that they do not obtain mercy, and that the word fails to produce its effect on them, so as to soften their minds to repentance.

So is the kingdom of God. Though this comparison has the same object as the two immediately preceding, Christ appears to direct his discourse purposely to the ministers of the word, so that they may not grow indifferent about the discharge of their duty, because the fruit of their labor does not immediately appear.

He holds out for their imitation the example of farmers, who throw seed into the ground with the expectation of reaping, and do not torment themselves with uneasiness and anxiety, but go to bed and rise again; or, in other words, pursue their ordinary and daily toil, until the corn reaches maturity in due season.

In like manner, though the seed of the word may be concealed and choked for a time, Christ enjoins pious teachers to be of good courage, and not to allow their alacrity to be diminished by distrust.