One of HarvestCall's Guiding Principles is to "promote a biblical understanding of outreach and service." While this certainly happens in general terms from pulpits Sunday after Sunday in our congregations, it is beneficial to have focused learning and tools on specific topics.
The starting point for sharing the gospel is truly understanding the gospel. It's a term we use often and most of us have a general grasp of it. But do we know it well enough to encourage ourselves in our faith, to teach it to our children, to bolster other believers, and to share it with the lost?
HarvestCall is working on a nine-part Bible study to equip the brotherhood to do this. A beta version of the first three chapters was tested with participants at our Columbia, SC rebuilding ministry project in winter 2017. Additional chapters are now in development.
What follows is HarvestCall's working definition of the gospel with amplified explanation and supporting verses.
Gospel Definition (with amplification)
The gospel is the good news of how fallen mankind can be reconciled to God by grace through faith in the redemptive work of his son Jesus, and transformed in heart and mind by the power of the Holy Spirit.
Adam and Eve died spiritually after they sinned by eating the forbidden fruit.  Their perfect relationship with God was over.  Adam’s spiritual death has been passed down to all humanity. We are all born spiritually dead, with a fallen nature — an ingrained tendency to sin.  Our sin separates us from God and puts us into bondage, which we of our own efforts are powerless to escape.
Because of sin, our relationship with God is broken.  When we place our faith in the redemptive work of Jesus and repent, Christ’s blood removes the sin and clears the way for a restored relationship and peace with God  –who adopts us into his family as sons and daughters. 
Grace through Faith
Salvation is received by grace through faith.  It is a free gift to all who will believe. It cannot be earned by any good works we might perform.  Because God is rich in love and mercy, he chose to make us alive in Christ.  The grace that comes through faith removes our rightful condemnation and mercifully transfers us from death to life. 
The redemptive work of his son Jesus
When Adam fell, God promised to send a Savior  and throughout the Old Testament he provided descriptions about this coming Messiah. Jesus fulfilled all the Old Testament prophecies and was obedient to the Father, completing the work which he sent him to do, including living without sin , shedding his blood as a sacrifice, being buried, and arising from the grave,  ascending to God’s right hand,  and sending his Holy Spirit.
Transformed in heart and mind (and) power of the Holy Spirit
Through repentance  and faith, God changes us from the inside out.  He gives us a new way of thinking.  He changes our heart  and our desires change as the Holy Spirit makes us more like the image of God.  As new creations we are no longer captive to sin , but are enabled to live holy and righteous lives, which is our reasonable service. 
Back to Gospel Definition
Grace: the unmerited favor of God toward man.
Repentance: a sorrowful turning from sin, towards the mercy of God
 But of the tree of the knowledge of good and evil, thou shalt not eat of it:for in the day that thou eatest thereof thou shalt surely die. (Genesis 2:17)
 Unto the woman he said, I will greatly multiply thy sorrow and thy conception; in sorrow thou shalt bring forth children; and thy desire shall be to thy husband, and he shall rule over thee. And unto Adam he said, Because thou hast hearkened unto the voice of thy wife, and hast eaten of the tree, of which I commanded thee, saying, Thou shalt not eat of it:cursed is the ground for thy sake; in sorrow shalt thou eat of it all the days of thy life; Thorns also and thistles shall it bring forth to thee; and thou shalt eat the herb of the field; In the sweat of thy face shalt thou eat bread, till thou return unto the ground; for out of it wast thou taken:for dust thou art, and unto dust shalt thou return (Genesis 3:16-19)
 Wherefore, as by one man sin entered into the world, and death by sin; and so death passed upon all men, for that all have sinned: (Romans 5:12)
 And you, that were sometime alienated and enemies in your mind by wicked works, yet now hath he reconciled (Colossians 1:21)
 For if, when we were enemies, we were reconciled to God by the death of his Son, much more, being reconciled, we shall be saved by his life. (Romans 5:10)
Back to Gospel Definition
 But when the fulness of the time was come, God sent forth his Son, made of a woman, made under the law, To redeem them that were under the law, that we might receive the adoption of sons (Galatians 4:4-5)
 For by grace are ye saved through faith; and that not of yourselves:it is the gift of God: Not of works, lest any man should boast (Ephesians 2:8-9)
 Not by works of righteousness which we have done, but according to his mercy he saved us, by the washing of regeneration, and renewing of the Holy Ghost; Which he shed on us abundantly through Jesus Christ our Saviour; That being justified by his grace, we should be made heirs according to the hope of eternal life (Titus 3:5-7)
 Even when we were dead in sins, hath quickened us together with Christ, (by grace ye are saved;) (Ephesians 2:5)
 Verily, verily, I say unto you, He that heareth my word, and believeth on him that sent me, hath everlasting life, and shall not come into condemnation; but is passed from death unto life. (John 5:24)
Back to Gospel Definition
 And I will put enmity between thee and the woman, and between thy seed and her seed; it shall bruise thy head, and thou shalt bruise his heel. (Genesis 3:15)
 For we have not an high priest which cannot be touched with the feeling of our infirmities; but was in all points tempted like as we are, yet without sin. (Hebrews 4:15)
 Take heed therefore unto yourselves, and to all the flock, over the which the Holy Ghost hath made you overseers, to feed the church of God, which he hath purchased with his own blood. (Acts 20:28)
For I delivered unto you first of all that which I also received, how that Christ died for our sins according to the scriptures; And that he was buried, and that he rose again the third day according to the scriptures (1 Corinthians 15:3-4)
 Who is he that condemneth? It is Christ that died, yea rather, that is risen again, who is even at the right hand of God, who also maketh intercession for us. (Romans 8:34)
 Repent ye therefore, and be converted, that your sins may be blotted out, when the times of refreshing shall come from the presence of the Lord; (Acts 3:19)
Back to Gospel Definition
 Therefore if any man be in Christ, he is a new creature:old things are passed away; behold, all things are become new. (2 Corinthians 5:17)
 And be not conformed to this world:but be ye transformed by the renewing of your mind, that ye may prove what is that good, and acceptable, and perfect, will of God (Romans 12:2)
 A new heart also will I give you, and a new spirit will I put within you:and I will take away the stony heart out of your flesh, and I will give you an heart of flesh. (Ezekiel 36:26)
 But we all, with open face beholding as in a glass the glory of the Lord, are changed into the same image from glory to glory, even as by the Spirit of the Lord. (2 Corinthians 3:18)
 Knowing this, that our old man is crucified with him, that the body of sin might be destroyed, that henceforth we should not serve sin. (Romans 6:6)
 I beseech you therefore, brethren, by the mercies of God, that ye present your bodies a living sacrifice, holy, acceptable unto God, which is your reasonable service. (Romans 12:1)