I am not ashamed, for I know whom I have believed and am persuaded that He is able to keep what I have committed to Him until that Day. – 2 Timothy 1:12

It used to be a fashion, and I fear in some quarters still, to think that mistrust of our own condition, and doubt concerning our own salvation, is a kind of virtue. I have met with good people, who would not say that they were saved; they “hoped” that they were; and I have met with others who were not sure that they were cleansed by the precious blood of Christ; they “trusted” that they were. This state of mind is not a credit either to Christ, or to ourselves. If I told my son something, and he were to say to me, “I hope you will keep your word, father,” I should not feel that he treated me as he ought. Surely, to believe Christ up to the hilt is the way to honour Him. If we are one with Him, we lose the comfort of it if we do not know certainly the fact of our blessed union; we miss much of the confidence that comes of it if we do not clearly apprehend the reality; and we are robbed of much of the joy which it brings, and how little of the meaning of that word “the joy of the Lord is your strength,” unless we believe simply like children, and take the word to mean what it says, and are certain about it. This is an age of doubt; but, as for me, I will have none of it; I have doubted enough, and more than enough; I have done with it long ago; and I can say with Paul, “I know whom I have believed, and am persuaded that He is able to keep which I have committed unto Him against that day.” Salvation is by faith. Damnation comes by doubt. Doubt is the death of all comfort, the destruction of all force, the enemy of God and man. ~ C.H. Spurgeon

https://www.blueletterbible.org/comm/spurgeon_charles/sermons/2244.cfm