And he said, “Lord, I believe.” And he worshipped Him. – John 9:38

For with the heart one believes unto righteousness, and with the mouth confession is made unto salvation. – Romans 10:10

True faith always expresses itself to the Lord. This man, when he had believed in Jesus, said, “Lord, I believe.” True faith ought also to express itself to men, as Paul puts it, in writing to the Romans, “For with the heart man believeth unto righteousness; and with the mouth confession is made unto salvation;” or, as the Master Himself puts it, “He that believeth and is baptized shall be saved.” Therefore, the confession before men ought not to be neglected in any case; yet I fear, and hope, that there are some pilgrims who steal into heaven, scarcely known by men to be Christians, at least, not avowed as such by open profession. I do not recommend that dodging behind the hedges and getting to heaven along back roads; that is a bad plan, but, still, I trust some have managed it, though with much trouble and loss to themselves; but, in every case, every one who has believed has made the confession of that faith to the Master Himself. He has said to Jesus, as this man did, “Lord, I believe,” even though he has added, with another man, “Help Thou mine unbelief.” He has said to Jesus, with Thomas, “My Lord and my God.” There has been a personal acknowledgment, as we sometimes sing it:

“My faith looks up to Thee,
Thou Lamb of Calvary,
Savior divine.”

How sweetly doth faith, sometimes, come up from the wilderness, leaning upon her Beloved, and owning to Him that she is His, and He is hers! She cannot help making this confession; she would be untrue to herself and to her Lord if she did not do so. ~ C.H. Spurgeon

https://www.blueletterbible.org/Comm/spurgeon_charles/sermons/2667.cfm

“…for I know whom I have believed, and am persuaded that He is able to keep that which I have committed unto Him against that day.” – 2 Timothy 1:12

I could never be content without unquestioning certainty as to my soul’s salvation. Do you think that is more than a man ought to wish for? Are any of you at ease while you are afraid that you have a mortal disease working within you? Oh, no! You want to know, from a qualified physician, the truth about your case. And if it were whispered in your ear, at this moment, that your house was being broken into or was on fire, would you sit still here, and not trouble yourself as to whether the report were true or not? Would you not want to go at once, and see for yourself. If you knew that you bought an estate, some time ago, but you have since heard that the title to it is a very uncertain one, in fact, that, in all probability, you will lose all you have paid for it, would you not say, “I ought to have taken care to be certain about the title, and I would not have bought the estate if I had not felt that the deeds relating to it were all right”. Well, then, if you desire certainty about your bodily health, and about the safety of your house, and about the validity of your title-deeds, can you afford to go without certainty as to your soul’s affairs? No, you cannot; therefore, rest not till you have it. If you have various questions about your spiritual condition, boldly face those questions, and answer them; but never let any questions about your eternal welfare be such that you dare not face them, and do not wish to search out the answers to them. Pry to the very bottom of them; and, better still, ask the Lord to search you, and know your heart, to try you, and know your thoughts, and to lead you in the way everlasting; and be not content till you can truthfully say, “I know whom I have believed, and am persuaded that He is able to keep that which I have committed unto Him.”~ C.H. Spurgeon

https://www.blueletterbible.org/Comm/spurgeon_charles/sermons/2667.cfm

He answered and said, “Who is He, Lord, that I might believe on Him?” – John 9:36

Saving faith is that which rests upon a knowledge of Him. This man said to Jesus, “Who is He, Lord, that I might believe on Him?” He was not one whose notion of faith was that he need not know what he believed. The Church of Rome seems to inculcate some kind of implicit faith (or credulity) which can exist apart from knowledge; but how can I believe that which I do not know? Paul puts it thus, “Faith cometh by hearing.” You must first hear and know what it is you are to believe before you can believe it; otherwise, your faith is vain, like that of the man of whom I have sometimes spoken, who said, “I believe what the Church believes.” “But what does the Church believe?” It believes what I believe.” “Then what do you and the Church believe?” “Why, we both believe the same thing.” That is not the kind of believing that can save the soul. It is through the knowledge of Christ that we are saved. To know Christ is sometimes said to be analogous to believing in Christ. You must know what it is that you have to believe; a faith that does not know is no faith at all. Read through the Epistles of John, and mark with your pencil every time the word “know” is used. The apostle makes that word “know” come in again and again, for a man must know that which he is to believe and hence this man says to Christ, “Who is He, Lord, that I might believe on Him?”~ C.H. Spurgeon

https://www.blueletterbible.org/Comm/spurgeon_charles/sermons/2667.cfm

Jesus heard that they had cast him out; and when He had found him, He said unto him, “Dost thou believe on the Son of God?” He answered and said, “Who is He, Lord, that I might believe on Him?” And Jesus said unto him, “Thou hast both seen Him, and it is He that talketh with thee.” And he said, “Lord, I believe.” And he worshipped Him. – John 9:35-38

Now, strange to say, here is a pressed man; for I do not think that this man, whose eyes had been opened by Christ, had thought of becoming a believer in the Son of God until the Lord Jesus found him out. Before he had reached that point; indeed, before he knew that the Prophet who had opened his eyes was the Son of God, the Pharisees had cast him out of the synagogue, so that he was compelled to bear the cross for Christ although he did not then fully know Christ, and certainly had not believed upon the Son of God. Yet, in his case also, it appears that he cheerfully took up the cross which had been at the first forcibly laid upon him…This man, then, bearing Christ’s cross in a certain way, was cast out of the synagogue, and then Christ found him, and blessed him.

Observe, dear friend, where Christ began with him; for it will show us where and how the blessing usually enters. The door by which the richest of heaven’s favors must come to us is indicated by our Lord going to that door, and opening it. He said to the man, “Dost thou believe on the Son of God.” So that faith in the Son of God is the gate of benediction. Faith is that window of agate and gate of carbuncle by which the divine light of Jesus’ love comes streaming into the soul…So, in this enquiry of our Lord, we have most instructive teaching. His object, no doubt, was to bless this man by working in him saving faith, and therefore He said to him, “Dost thou believe on the Son of God?” ~ C.H. Spurgeon

https://www.blueletterbible.org/Comm/spurgeon_charles/sermons/2667.cfm