15 For this reason He is the mediator of a new covenant, so that, since a death has taken place for the redemption of the transgressions that were committed under the first covenant, those who have been called may receive the promise of the eternal inheritance. Hebrews 9:15 (NASB)
The Gospel is explained very well in the New Testament. The role of the Church in the World from the time of Christ’s Ascension until His return is very well defined for us there as well (to go and make disciples from all the earth, teaching them to observe all that He taught…) This Great Commission is not to ‘be the Gospel’ nor is it to ‘redeem the earth’ nor is it to ‘make the world a better place.’
No, it is to go and tell the Good News that we have a mediator of a new covenant and those who are called may receive the promised eternal inheritance that is made possible through the death of their Saviour who has redeemed through the shedding of His blood (see the passage above). You see, this is the Good News. The Gospel is to preach what Christ has done not what people have done, not what churches have done, not what religion has done or what being religious can do for anyone. It is simply to proclaim this message relying on the power and work of the Holy Spirit to draw those called to saving faith. Let’s take a closer look at this “redemption.” The word redemption in Hebrews 9:15 (above) translates απολυτρωσιν the Accusative, Singular form of ἀπολύτρωσις (apolutrōsis), which means “redemption, ransom.” Jesus died as a ransom to set free from sin those called.
This redemption is provided by Christ through His death on the cross (Romans 3:24; 1 Corinthians 1:30). In Ephesians 1:9; Colossians 1:14, it describes something that believers have right now. But in the remaining uses of this word (Luke 21:28; Romans 8:23; Ephesians 1:14; 4:30), there is a future aspect to redemption, which the called will not experience fully until Jesus returns again. It is made clear in these passages that this delay does not in any way put their redemption into jeopardy. The reason is that they have the Holy Spirit as a deposit guaranteeing their final redemption.