"Repent ye, and believe the gospel."— Mark 1:15

Below are snipets from a sermon that Charles Spurgeon preached on July 13th, 1862. The headings are mine as are anything in italics. Click on the title to see the full sermon by spurgeon.

JESUS PREACHED IT WITHOUT APOLOGY
Jesus preacheth with all the earnestness of a new zeal, combined with all the wisdom of a long preparation; in the beauty of holiness from the womb of morning he glittereth with the dew of his youth. Hear, O heavens, and give ear, O earth, for Messias speaketh in the greatness of his strength. He crieth unto the sons of men, "Repent ye, and believe the gospel." Let us give our ears to these words which, like their author, are full of grace and truth. Before us we have the sum and substance of Jesus Christ's whole teaching.

"Repent ye" is as much a command of God as "Thou shalt not steal." "Believe on the Lord Jesus Christ" has as fully a divine authority as "Thou shalt not murder." Why has the Lord made it a command to us to believe in Christ? There is a blessed reason. Many souls would never venture to believe at all if it were not made penal to refuse to do so. For this is the difficulty with many awakened sinners: may I believe? Have I a right to believe? Am I permitted to trust Christ? Now this question is put aside, once for all, and should never irritate a broken heart again. You are commanded by God to do it, therefore you may do it.

"Repentance is to leave

The sins we loved before,

And show that we in earnest grieve,

By doing so no more."

To repent does mean a change of mind; but then it is a thorough change of the understanding and all that is in the mind, so that it includes an illumination, an illumination of the Holy Spirit; and I think it includes a discovery of iniquity and a hatred of it, without which there can hardly be a genuine repentance.
 
FASLE REPENTANCE
Repentance is perfectly consistent with faith; and therefore we get the explanation of what repentance must be, from its being connected with the next command, "Believe the gospel." Any repentance that keeps thee from believing in Christ is a repentance that needs to be repented of; any repentance that makes thee think Christ will not save thee, goes beyond the truth and against the truth, and the sooner thou are rid of it the better. God deliver thee from it, for the repentance that will save thee is quite consistent with faith in Christ.
 
TRUE REPENTANCE
repentance that ejects sin as an evil tenant, and the faith which admits Christ to be the sole master of the heart; the repentance which purges the soul from dead works, and the faith that fills the soul with living works; the repentance which pulls down, and the faith which builds up; the repentance that scatters stones, and the faith which puts stones together; the repentance which ordains a time to weep, and the faith that gives a time to dance— these two things together make up the work of grace within, whereby men's souls are saved. The repentance which is here commanded is the result of faith; it is born at the same time with faith—they are twins. Now, a repentance which makes me weep and abhor my past life because of the love of Christ which has pardoned it, is the right repentance. Again, the repentance which makes us avoid present sin because of the love of God who died for us, this also is saving repentance.
 
REPENT AND BELIEVE IS A REASONABLE COMMAND
Is it an unreasonable thing to demand of a man that he should repent? You have a person who has offended you; you are ready to forgive him; do you think it is at all exacting or overbearing if you ask of him an apology; if you merely ask him, as the very least thing he can do, to acknowledge that he has done wrong? "No," say you, "I should think I showed my kindness in accepting rather than any harshness in demanding an apology from him." So God, against whom we have rebelled, who is our liege sovereign and monarch, seeth it to be inconsistent with the dignity of his kingship to absolve an offender who expresseth no contrition.
 
And then, again, believing; is that an unreasonable thing to ask of you? For a creature to believe its Creator is but a duty; altogether apart from the promise of salvation, I say, God has a right to demand of the creature that he has made, that he should believe what he tells him. And what is it he asks you to believe? Anything hideous, contradictory, irrational? It may be above reason, but it is not contrary to reason. He asks you to believe that through the blood of Jesus Christ, he can still be just, and yet the justifier of the ungodly. He asks you to trust in Christ to save you. Can you expect that he will save you if you will not trust him?
 
URGENCY
Last night there was a review on Wimbledon Common, and living not very far away from it, I could hear in one perpetual roll the cracks of the rifles and the thunder of cannon. One remarked to me, "Supposing there really were war there, we should not sit quite so comfortably in our room with our window open, listening to all this noise." No; and so when people come to chapel, they hear a sermon about repentance and faith; they listen to it. "What do you think of it?" "Oh—very well." But suppose it were real; suppose they believed it to be real, would they sit quite so comfortably? Would they be quite so easy? Ah, no! But you do not think it is real. You do not think that the God who made you actually asks of you this day that you should repent and believe.