5:9-12 Nothing can be more absurd than the conduct of those who doubt as to the truth of Christianity, while in the common affairs of life they do not hesitate to proceed on human testimony, and would deem any one out of his senses who declined to do so. The real Christian has seen his guilt and misery, and his need of such a Saviour. He has seen the suitableness of such a Saviour to all his spiritual wants and circumstances. He has found and felt the power of the word and doctrine of Christ, humbling, healing, quickening, and comforting his soul. He has a new disposition, and new delights, and is not the man that he formerly was. Yet he finds still a conflict with himself, with sin, with the flesh, the world, and wicked powers. But he finds such strength from faith in Christ, that he can overcome the world, and travel on towards a better. Such assurance has the gospel believer: he has a witness in himself, which puts the matter out of doubt with him, except in hours of darkness or conflict; but he cannot be argued out of his belief in the leading truths of the gospel. Here is what makes the unbeliever's sin so awful; the sin of unbelief. He gives God the lie; because he believes not the record that God gave of his Son. It is in vain for a man to plead that he believes the testimony of God in other things, while he rejects it in this. He that refuses to trust and honour Christ as the Son of God, who disdains to submit to his teaching as Prophet, to rely on his atonement and intercession as High Priest, or to obey him as King, is dead in sin, under condemnation; nor will any outward morality, learning, forms, notions, or confidences avail him.

12. the Son … life—Greek, "THE life." Bengel remarks, The verse has two clauses: in the former the Son is mentioned without the addition "of God," for believers know the Son: in the second clause the addition "of God" is made, that unbelievers may know thereby what a serious thing it is not to have Him. In the former clause "has" bears the emphasis; in the second, life. To have the Son is to be able to say as the bride, "I am my Beloved's, and my Beloved is mine" [So 6:3]. Faith is the mean whereby the regenerate HAVE Christ as a present possession, and in having Him have life in its germ and reality now, and shall have life in its fully developed manifestation hereafter. Eternal life here is: (1) initial, and is an earnest of that which is to follow; in the intermediate state (2) partial, belonging but to a part of a man, though that is his nobler part, the soul separated from the body; at and after the resurrection (3) perfectional. This life is not only natural, consisting of the union of the soul and the body (as that of the reprobate in eternal pain, which ought to be termed death eternal, not life), but also spiritual, the union of the soul to God, and supremely blessed for ever (for life is another term for happiness) [Pearson, Exposition of the Creed].