"A man does not possess Christ by faith in the way he possesses money in his cupboard or deeds of land, which he takes for granted that he has and yet perhaps never looks at once a year. No, Christ is as meat that a man feeds on, chews, and digests, and whose stomach works on continually. The man lives on Him every day; that is the application of faith (John 6:53). If other bread is our daily food, then surely Christ is much more; therefore it is called the life of faith: “The life I live is by the faith on the Son of God” (Gal. 2:20). Life is a continuation of action and motion; as the heart is the principle of life — it always beats, and if it lies still a man dies — such is faith. Faith is not a sleeping thing, nor merely not doubting that Christ is mine, but a continual active whetting of my thoughts on Christ as mind, or casting myself upon Him to be mine. It is living on Him and in Him.
Some men live in a good opinion of themselves and are confident that Christ is theirs; they are not sued or troubled in this confidence by Satan’s temptations, and no doubts come to put them out of a sense of possession. This they account to be faith and take for granted that they shall never be cast out.
In practice, many understand faith to be belief and persuasion only, so they make faith a good persuasion and opinion of their present condition. The object and goal of their faith is their own estate, and not Christ and His love, so their faith is not a good opinion of Him or founded on the daily thoughts they have of His merit, satisfaction, mercy, grace, righteousness, etc. Their faith is a good opinion of their themselves, arising out of the self-flattery of their own hearts, so that they honor not Christ in their thoughts so much as themselves; theirs is a judgment of charity to themselves rather than faith in Christ. I call it that charitable opinion that one Christian is bound to have of others, the assumption that they are the children of God, that their eternal state is good, and that they are in Christ. Such a charitable opinion of themselves, whereby, as the apostle says of the Hebrews, they are persuaded of good things concerning themselves, is the only faith of a great many people; but this is not to believe on Christ, but on themselves. The fact that their own estate is indeed the object of their faith is evident by this, that if any man goes about to discover his natural condition while he is without true faith, he soon becomes upset, and says, “You would bring me to unbelief and despair.” This is because an apprehension that his present state is good is that, and all that, which he reckons as faith. But those who seek his good would bring him from a false belief about his state and himself to a good and a true belief in Christ, and on God’s free grace, which are the prime objects of faith." (Thomas Goodwin, The Object and Acts of Justifying Faith, Works 8:331-332)