Could do nothing - Could do no such work as this. This reasoning was conclusive. The fact that Jesus could perform miracles like this was full proof that he was commissioned by God - proof that never has been and never can be refuted. One such miracle proves that he was from God. But Jesus gave many similar proofs, and thus put his divine mission beyond the possibility of doubt.

If this man were not of God, etc. - A very just conclusion: God is the fountain of all good: all good must proceed from him, and no good can be done but through him; if this person were not commissioned by the good God, he could not perform such beneficent miracles as these.

If this man were not of God,.... If he had not his mission, commission, and credentials from God; if he had not been sent by him, and had not authority from him, and was not assisted by him, as man, or God was not with him,

he could do nothing; or "not do these things", as the Syriac version reads; that is, such miraculous works; or, as the Persic version, "he could not do this miracle": open the eyes of a man born blind. His doing this is a full proof that he is of God, and comes from him.

If this man were not of God, he could do nothing.

9:30-33 Why herein is a marvellous thing. It was also a marvellous thing that one who was a blind beggar a few hours before should now expound theology to the very men that sat in Moses' seat (Mt 23:2) and show a better knowledge of the spirit of the Scriptures than the great ecclesiastics. Without the power of God no man could open the eyes of one born blind.

9:33 He could do nothing - Of this kind; nothing miraculous.

9:24-34 As Christ's mercies are most valued by those who have felt the want of them, that have been blind, and now see; so the most powerful and lasting affections to Christ, arise from actual knowledge of him. In the work of grace in the soul, though we cannot tell when, and how, and by what steps the blessed change was wrought, yet we may take the comfort, if we can say, through grace, Whereas I was blind, now I see. I did live a worldly, sensual life, but, thanks be to God, it is now otherwise with me, Eph 5:8. The unbelief of those who enjoy the means of knowledge and conviction, is indeed marvellous. All who have felt the power and grace of the Lord Jesus, wonder at the wilfulness of others who reject him. He argues strongly against them, not only that Jesus was not a sinner, but that he was of God. We may each of us know by this, whether we are of God or not. What do we? What do we for God? What do we for our souls? What do we more than others?