The following is a helpful summary of The Christian's Great Interest prepared by William Guthrie. The language has been slightly updated for the benefit of understanding.
Q. 1. What is the great business a man has to do in this world?
A. To make sure of a saving interest in Christ Jesus, and to live in a way that is consistent with it.
Q. 2. Have not all the members of the visible church a saving interest in Christ?
A. No, in truth only a very few of them have it.
Q. 3. How shall I know if I have a saving interest in Him?
A. Ordinarily the Lord prepares His own way in the soul by a work of humiliation, and shows a man's sin and misery to him, and exercises Him so much with it, that He longs for Christ Jesus, the physician.
Q. 4. How shall I know if I have got a true sight of my sin and misery?
A. A true sight of sin makes a man take salvation to heart above anything in this world. It makes him reject all relief in himself, seen in his best things: it makes Christ who is the Redeemer, very precious to the soul: it makes a man afraid to sin afterwards, and makes him content to be saved upon any terms that God pleases.
Q. 5. By what other ways may I discern a saving interest in him?
A. By the going out of the heart seriously and affectionately towards Him, as He is held out in the gospel; and this is faith or believing.
Q. 6. How shall I know if my heart goes out after Him aright, and that my faith is true saving faith?
A. Where the heart goes out aright after Him in true and saving faith, the soul is pleased with Christ alone above all things, and is satisfied with Him in all Him three offices, to rule and instruct as well as to save; and is content to cleave unto Him, whatever difficulties may follow.
Q. 7. What other mark of a saving interest in Christ can you give me?
A. He that is in Christ savingly, is a new creature. He is graciously changed and renewed in some measure, in the whole man, and in all his ways pointing towards all the known commands of God.
Q. 8. What if I find sin now and then prevailing over me?
A. Although every sin deserves everlasting vengeance, yet, if you are afflicted for your failings and confess them with shame of face unto God, honestly resolving to strive against them from now on, and seek pardon from Christ, you shall obtain mercy and your interest stands sure.
Q. 9. What shall the man do who cannot lay claim to Christ Jesus nor any of those marks spoken of it?
A. Let him not rest until he makes sure of a saving interest in Christ.
Q. 10. What way can a man make sure of an interest in Christ, who never had a saving interest in Him hitherto?
A. He must take his sins to heart, and the great danger into which they have brought him and he must take to heart God's offer of pardon and peace through Christ Jesus, and heartily close with God's offer by retaking himself unto Christ, the blessed refuge.
Q. 11. What if my sins are especially heinous and worse than the ordinary?
A. Whatever your sins may be, if you will close with Christ Jesus by faith, you will never enter into condemnation.
Q. 12. Is faith in Christ only required of men?
A. Faith is the only condition upon which God does offer peace and pardon unto men; but be assured, faith, if it be true and saving, will not be alone in the soul, but will be attended with true repentance, and a thankful pursuit of conformity to God's image.
Q. 13 How shall I be sure that my heart does accept of God's offer, and does close with Christ Jesus?
A. Go and make a covenant explicitly and speak it all by word unto God.
Q. 14 How shall I do that?
A. Set apart some portion of time, and, having considered your own lost condition, and the remedy offered by Christ Jesus, work up your heart to be pleased and close with that offer, and say unto God expressly that you accept of that offer, and of Him to be your God in Christ; and give up yourself to Him to be saved in His way, without reservation or exception in any way; and that from now on you will wait for salvation in the way that He has appointed.
Q. 15 What if I break with God afterwards?
A. You must resolve in His strength not to break, and watch over your own ways, and put your heart in His hand to keep it and if you break, you must confess it unto God, and judge yourself for it, and flee to the Advocate for pardon, and resolve to do so no more: and you must do this as often as you fail.
Q. 16 How shall I come to full assurance of my interest in Christ, so that it may be beyond question?
A. Learn to lay your weight upon the blood of Christ, and study purity and holiness in all kinds of conduct: and pray for the witness of God's Spirit to join with the blood and the water; and His testimony added unto these will establish you in the faith of an interest in Christ.
Q. 17. What is the consequence of such closing with God in Christ by heart and mouth?
A. Union and communion with God, every good here and His blessed fellowship in heaven forever afterwards.
Q. 18. What if I slight all these things, and do not lay them to heart to put them in practice?
A. The Lord comes with His angels, in flaming fire, to render vengeance to them who obey not His gospel; and your judgement shall be greater than that of Sodom and Gomorrah; and so much the greater that you have read this book, for it shall be a witness against you in that day.