And when the sun was up,.... Some time, and its heat was increasing, and it began to shine out hot, and beat with some vehemency and strength; which may denote some sore temptation, or severe affliction, or fiery trial of persecution and tribulation; see Matthew 13:21 for this is not to be understood of the glorious light of the Gospel, which, though very comfortable and refreshing, as well as illuminating to good men, is very distressing and tormenting to carnal minds; they cannot bear its truths and doctrines; this is the fire which comes out of the mouth of God's faithful witnesses, and torments them that dwell on the earth, and devours their enemies, Revelation 11:5. And it, moreover, like the sun, has different effects on different objects; as the sun hardens clay, and melts wax, so the Gospel is to the hardening of some, and softening of others; to the one it is the savour of life unto life, and to the other the savour of death unto death; but this cannot be intended, because the word by these hearers is first received with joy. Nor is Christ the sun of righteousness meant, who arises with healing in his wings, and gives grace and glory to his people; but the sun of persecution and affliction, in which sense the metaphor is used, in Song 1:6 the heat of which the church patiently bore, though she was made black with it: but these hearers think it strange that such a fiery trial should befall them; wherefore, as they take up their profession in haste, they as quickly drop it; see Revelation 7:16.
They were scorched, and because they had not root, they withered away: they were offended with what they met with, for the sake of Christ, and the profession of his word; and therefore, not being rooted in him, nor in the love of God, nor having the root of the matter, true grace, in themselves, or, as Luke says, "lacked moisture", of divine grace, of the dews and waterings of it, fell away finally and totally. This is no instance of the apostasy of real saints, or any proof of true believers falling away finally and totally; since these were not rooted, and grounded in the everlasting and unchangeable love of God, were not interested in it, or were partakers of the effects of it; had they been so, they could never have been separated from it; tribulation, distress, and persecution could never have done it; none of these would ever have moved them; had they had the love of God shed abroad in their hearts, they would have gloried in tribulation: nor were they united to Christ, rooted and built up in him; had they, they would have continued to have derived life and nourishment from him; in him the life of believers is hid, and because he lives they live also; as long as there is life in the root, the branches will not die; he is the root that bears the branches, the root of the righteous that yields fruit, and is never moved: nor had these the truth of grace, which is an incorruptible seed, a well of living water springing up to everlasting life; had they, they could never have withered away; to such God gives more grace, he himself is as the dew unto them, and he waters them every moment.

And when the sun was up they were scorched. It was not rooted in that deep, moist soil which would have enabled it to resist the scorching heat of the sun.