Whether he be a sinner, I know not. The blind man appears not to have been at all prevented by fear from giving a sincere testimony. For there is no reason to believe that he had any doubts about Christ, as his words seem to imply; but I rather think that he spoke ironically, in order to wound them more deeply. He had already confessed that Christ was a Prophet, (verse 17.) Perceiving that he gains nothing by doing so, he suspends his judgment about the person, and brings forward the fact itself, so that, while he makes this admission in their favor, he is not free from ridiculing them.

Whether he be a sinner or no, I know not - The man had just said that he believed Jesus to be a prophet, John 9:17. By his saying that he did not know whether he was a sinner may be meant that though he might be a prophet, yet that he might not be perfect; or that it did not become him, being an obscure and unlearned man, to attempt to determine that question. What follows shows that he did not believe that he was a sinner, and these words were probably spoken in irony to deride the Pharisees. They were perverse and full of cavils, and were determined not to believe. The man reminded them that the question was not whether Jesus was a sinner; that, though that might be, yet it did not settle the other question about opening his eyes, which was the chief point of the inquiry.
One thing I know - About this he could have no doubt. He disregarded, therefore, their cavils. We may learn, also, here:
1. That this declaration may be made by every converted sinner. He may not be able to meet the cavils of others. He may not be able to tell how he was converted. It is enough if he can say, "I was a sinner, but now love God; I was in darkness, but have now been brought to the light of truth."
2. We should not be ashamed of the fact that we are made to see by the Son of God. No cavil or derision of men should deter us from such an avowal.
3. Sinners are perpetually shifting the real point of inquiry. They do not inquire into the facts. They assume that a thing cannot be true, and then argue as if that was a conceded point. The proper way in religion is first to inquire into the facts, and then account for them as we can.

Whereas I was blind, now I see - He pays no attention to their cavils, nor to their perversion of justice; but, in the simplicity of his heart, speaks to the fact, of the reality of which he was ready to give them the most substantial evidence.

He answered and said,.... That is, the man who had been blind, who takes no notice of the confession they pressed him to, which is what he could not do; there being no collusion in this case, he only replies to the reproachful character they had given of his benefactor.
Whether he be a sinner or not, I know not: or "if he is a sinner I know not", as the Vulgate Latin version renders it, suggesting that he did not know he was a sinner; he could not charge him with being one; nor could he join with them in saying he was a sinner; nor did he think and believe he was: however, he was sure he had done a good thing to him, and in that he was no sinner; and what proof they had of his being one he could not tell: and be that as it will, adds he,
one thing I know, that whereas I was blind, now I see; as if he should say, whatever charges you bring against the person that has done me this favour, which I am not able to answer to, you cannot reason me out of this; this I am sure of, that once I had no eyes to see with, and now I have, and that by the means of this man you reproach. And so it is with persons enlightened in a spiritual sense, whatever things they may be ignorant of, though they may not know the exact time of their conversion, nor have so much Gospel light and knowledge as others, or be so capable of expressing themselves, or giving such a distinct and orderly account of the work of God upon them as some can, nor dispute with an adversary for the truths of the Gospel, or have that faith of assurance, and discoveries of God's love, and the application of such great and precious promises as others have; yet this they know, that they were once blind, as to the knowledge of spiritual things, as to a saving knowledge of God in Christ, as to a true sight and sense of themselves, their sins and lost estate, as to the way of righteousness and salvation by Christ, or the work of the Spirit of God upon their souls, or as to any true and spiritual discerning of the Scriptures, and the doctrines of grace in them: but now they are comfortably assured, they see the exceeding sinfulness of sin, the plague of their own hearts, the insufficiency of their righteousness to justify them before God, and the beauty, fulness, suitableness, and ability of Christ as a Saviour; and that their salvation is, and must be of free grace; and that they see the truths of the Gospel in another light than they did before, and have some glimpse of eternal glory and happiness, in the hope of which they rejoice.

He answered and said, Whether he be a sinner or no, &c.--Not that the man meant to insinuate any doubt in his own mind on the point of His being "a sinner," but as his opinion on such a point would be of no consequence to others, he would speak only to what he knew as fact in his own case.