And should sleep, and rise night and day - Should sleep in the night and rise by day, for so the expression is to be understood. That is, should live in his usual way, without exerting any influence over the growing grain. By this we are not to infer that men are to use no diligence in the obtaining and in the growth of piety; but the illustration shows only that as we cannot tell how grain grows, so we cannot tell the mode in which piety increases in the heart.
He knoweth not how - This is still true. After all the researches of philosophers, no one has been able to tell the way in which grain grows. They can observe one fact after another; they can see the changes; they can see the necessity of rains and suns, of care and shelter, but beyond this they cannot go. So in religion. We can mark the change; we can see the need of prayer, and self-examination, and searching the Scriptures, and the ordinances of religion, but we cannot tell in what way the religious principle is developed and strengthened. As God unseen, yet by the use of proper means, makes the grass to flourish, so God unseen, but by proper means, nourishes the soul, and the plants of piety spring up, and bloom, and bear fruit. Compare the notes at John 3:8.

And should sleep and rise night and day - That is, he should sleep by night, and rise by day; for so the words are obviously to be understood.
He knoweth not how - How a plant grows is a mystery in nature, which the wisest philosopher in the universe cannot fully explain.

And (g) should sleep, and rise night and day, and the seed should spring and grow up, he (h) knoweth not how.
(g) That is, when he has finished sowing should wait both day and night not doubting that the seed should spring forth, which grows both by day and night.
(h) It is the duty of the ministers to work the ground with all diligence, and accredit the success to God: for the mighty work of the seed coming to blade and ear is mysterious, and is only known by the fruit that comes.

And should sleep,.... That is, the man that casts in the seed, who represents the ministers of the Gospel: and, as applied to them, is not to be understood of natural sleep, and indulging themselves in that; much less of spiritual sloth and indolence, as if they cared not what became of the seed sown, whether it sprung up, and came to any thing, or not; for neither of these belong to the characters of the true ministers of the word: for though bodily sleep in them, as in other men, is necessary for the support of nature, and to put them in a capacity of discharging their work; yet perhaps none have less of it than studious and laborious preachers of the Gospel; and much less do they indulge a spiritual sleep and slothfulness; though this may sometimes attend them, as well as others: but then, whilst they sleep, in this sense, tares are sown, and they spring up, and not the good seed of the word, as in this parable; besides, as they labour in the word and doctrine, by studying and preaching it, so they follow their ministrations with incessant prayers that they be succeeded to the conversion of sinners, and comfort of saints; nor can they be easy, unless they have some seals of their ministry: but rather, this may be understood of the sleep of death; for so it often is, that the seed sown by them does not appear in the fruits of it to the churches of Christ, among whom they have ministered, until after they are fallen asleep in Jesus: though it seems best to understand it of their holy security, confidence, and satisfaction in their own minds, that it will turn to profit and advantage, both to the good of souls, and glory of God, not despairing of success; but having left their work with their Lord, they sit down easy and satisfied, believing that the word shall prosper to the thing whereunto it is sent:
and rise night and day; which shows their diligence and laboriousness, and their constant attendance to other parts of their work, rising up early, and sitting up late, to prepare for, and discharge their ministerial work; and their continued expectation of the springing-up of the seed sown, which accordingly does in proper time:
and the seed should spring and grow up, he knoweth not how; it is a mystery in nature, how the seed under the clods, where it dies before it is quickened, should spring and grow up, and bring forth fruit; and so it is in grace, how the word of God first operates on a sinner's heart, and becomes the ingrafted word there; the time when, and much less the manner how, grace, by this means, is implanted in the heart, are not known to a soul itself, and still less to the ministers of the word, who sometimes never know any thing of it; and when they do, not till some time after: this work is done secretly, and powerfully, under the influence of divine grace, without their knowledge, though by them as instruments; so that though the sowing and planting are theirs, all the increase is God's: this may encourage attendance on the ministry of the word, and teach us to ascribe the work of conversion entirely to the power and grace of God.

Should sleep, and rise, etc. While giving the seed sown time to germinate and come forth.