"Examine yourselves, whether ye be in the faith." Oh! says one, "You may examine me whether I am in the faith; I am an orthodox Christian, fully up to the standard, good genuine weight; there is no fear whatever of my coming up to the mark, and going a little beyond it too." Ah! but, my friend, that is not the question; I would have you orthodox, for a man who is heterodox in his opinions, will most likely be heterodox in his actions; but the question now is not whether you believe the truth—but whether you are in the truth? Just to give you an illustration of what I mean. There is the ark; and a number of men around it. "Ah!" says one, I believe that ark will swim." "Oh!" says another, "I believe that ark is made of gopher-wood, and is strong from stem to stern; I am quite sure that ark will float, come what may; I am a firm believer in that ark." Ay, but when the rain descended, and the flood came, it was not believing the ark as a matter of fact—it was being in the ark that saved men, and only those that were in it escaped in that dread day of deluge. So there may be some of you that say of the gospel of Christ, "I believe it to be of a particular character," and you may be quite correct in your judgment; you may say, "I think it to be that which honours God, and casts down the pride of man;" herein too you may think quite right; but mark, it is not having an orthodox faith, but it is being in the faith, being in Christ, taking refuge in Him as in the ark; for he that only has the faith as a thingab extra, and without being in the faith, shall perish in the day of God's anger; but he that lives by faith, he who feels that faith operates upon him, and is to him a living principle; he who realises that faith is his dwelling place, that there he can abide, that it is the very atmosphere he breathes and the very girdle of his loins to strengthen him,—such a man is in the faith. But, we repeat again, all the orthodoxy in the world, apart from its effect upon the heart as a vital principle, will not save a man. "Examine yourselves, whether ye be in the faith; prove your own selves."
"Know ye not your own selves?" If you do not, you have neglected your proper study. What avails all else that you do know, if you know not yourself? You have been roaming abroad, while the richest treasure was lying at home; you have been busying yourself with irrelevant affairs, while the main business has been neglected and ruined. "Know ye not your own selves?" And especially know ye not this fact, that Jesus Christ must be in your heart, formed and living there, or else ye are reprobates? That is, ye are worthless persons, vain pretenders, spurious professors; your religion is but a vanity and a show. "Reprobate silver shall men call you, because the Lord hath rejected you."
Now, what is it to have Jesus Christ in you? The Roman Catholic hangs the cross on his bosom; the true Christian carries the cross in his heart; and a cross inside the heart, my friends, is one of the sweetest cares for a cross on the back. If you have a cross in your heart—Christ crucified in you, the hope of glory—all the cross of this world's troubles will seem to you light enough, and you will easily he able to sustain it. Christ in the heart means Christ believed in, Christ beloved, Christ trusted, Christ espoused, Christ communed with, Christ as our daily food, and ourselves as the temple and palace wherein Jesus Christ daily walks. Ah! there are many here that are total strangers to the meaning of this phrase. They do not know what it is to have Jesus Christ in them. Though ye know a little about Christ on Calvary, ye know nothing about Christ in the heart. Now, remember, that Christ on Calvary will save no man, unless Christ be in the heart. The Son of Mary, born in the manger, will not save a soul, unless he be also born in your hearts, and live there—your joy, your strength, and your consolation. "Know ye not your own selves, how that Jesus Christ is in you, except ye be reprobates?"
C.H. Spurgeon, from his sermon entitled - 'self-examination' . I highly recommend reading the entire sermon.
"Afresh, precious, precious Jesus, I resign this body to You, for doing or suffering, for living or dying. Will You accept it? Will You use me for Your glory more than heretofore, that You may have some little return for all the benefits You have done to me? Oh, do grant this request; my heart longs for it, my spirit pleads for it; and "if You will, You can." You know the hot temptation of which I am the subject. Bring Your glory out of it, and keep me from the evil, and it shall be well." - Ruth Bryan