Jesus and the apostles preached the gospel well before Jesus’ death on the cross:
From that time Jesus began to preach, and to say, Repent: for the kingdom of heaven is at hand.
Matthew 4:17, 23
And Jesus went about all Galilee, teaching in their synagogues, and preaching the gospel of the kingdom, and healing all manner of sickness and all manner of disease among the people.
And as ye go, preach, saying, The kingdom of heaven is at hand.
Matthew 10:7
Now after that John was put in prison, Jesus came into Galilee, preaching the gospel of the kingdom of God,
Mark 1:14,15
And saying, The time is fulfilled, and the kingdom of God is at hand: repent ye, and believe the gospel.
And he said unto them, I must preach the kingdom of God to other cities also: for therefore am I sent.
Luke 4:43,44
And he preached in the synagogues of Galilee.
Then he called his twelve disciples together, and gave them power and authority over all devils, and to cure diseases.
Luke 9:1,2,6
And he sent them to preach the kingdom of God, and to heal the sick.
And they departed, and went through the towns, preaching the gospel, and healing every where.
What gospel was this?
Jesus hadn’t died yet. And people had to realize He was the Messiah on their own, with the help of the Holy Spirit revealing it to them.
What was the good news to be preached?
What was the message of John the Baptist?
That God will forgive you. If you repent, be baptized, and start living a different life – because the Kingdom of God was now near and there will be a Judgement where everyone’s works will be judged.
And saying, Repent ye: for the kingdom of heaven is at hand.
Matthew 3:2,6-8
And were baptized of him in Jordan, confessing their sins.
But when he saw many of the Pharisees and Sadducees come to his baptism, he said unto them, O generation of vipers, who hath warned you to flee from the wrath to come?
Bring forth therefore fruits meet for repentance.
What exactly does Repent mean?
To Repent means to be sorry for your sins, and to turn away from them, and start doing good things. See
https://www.merriam-webster.com/dictionary/repent
And what is the Kingdom of God/Kingdom of Heaven?
It is for God’s will to be done on Earth, as it is in Heaven, and this Kingdom is within you, given from above, if you just trust God. It is not His will that ANYONE should be lost!:
After this manner therefore pray ye: Our Father which art in heaven, Hallowed be thy name.
Matthew 6:9,10
Thy kingdom come. Thy will be done in earth, as it is in heaven.
And when he was demanded of the Pharisees, when the kingdom of God should come, he answered them and said, The kingdom of God cometh not with observation:
Luke 17:20,21
Neither shall they say, Lo here! or, lo there! for, behold, the kingdom of God is within you.
Now that Jesus has died and is our Advocate next to the Father, what are the very basic conditions of salvation?
Repent, and believe the One He has sent.
So what exactly do we need to do?
Truly be sorry for the sins we have committed, and honestly not want to do them anymore. Believe the Word and the everlasting gospel. We can become Sons of God through faith and the power of the cross:
But as many as received Him, to them gave he power to become the sons of God, even to them that believe on His name.
John 1:12
Why is power mentioned here? Through faith in Jesus’ sacrifice, and the power of God, we become a new creation. That’s why baptism is linked to the gospel, and also why John the Baptist baptized. It signifies death to our old way of life, and into a new way of life of living for God and others and doing God’s will.
This salvation, forgiveness, and power is a free gift. We no longer have a death sentence hanging over our heads due to our sins, because Jesus took our place. And we can ultimately defeat sin. That’s the GOOD NEWS.
For I am not ashamed of the gospel of Christ: for it is the power of God unto salvation to every one that believeth; to the Jew first, and also to the Greek.
Romans 1:16
But this is not the entire gospel. Most of the Christian world can’t seem to grasp the true, full gospel. There will be a Judgment, and we will have to answer to God for every word spoken and every deed done.
The evil one has done a masterful job confusing everyone on this. And most of the world tilts too far one way (faith) or the other (works).
To re-iterate, we are not saved by works. But faith without works is dead (see the entire book of James). Paul summarizes this nicely in Ephesians:
For by grace are ye saved through faith; and that not of yourselves: it is the gift of God:
Ephesians 2:8-10
Not of works, lest any man should boast.
For we are his workmanship, created in Christ Jesus unto good works, which God hath before ordained that we should walk in them.
At first glance this may seem confusing. Paul says we are not saved by works, but then he says in Christ we do good works and God has decreed that we walk in them.
We do and walk in good works using our faith. This is the essence of the New Covenant. It doesn’t nullify God’s Law (the Ten Commandments). It allows us to walk in them.
Jeremiah describes the New Covenant in Chapter 31:
Behold, the days come, saith the LORD, that I will make a new covenant with the house of Israel, and with the house of Judah:
Jeremiah 31:31-33
Not according to the covenant that I made with their fathers in the day that I took them by the hand to bring them out of the land of Egypt; which my covenant they brake, although I was an husband unto them, saith the LORD:
But this shall be the covenant that I will make with the house of Israel; After those days, saith the LORD, I will put my law in their inward parts, and write it in their hearts; and will be their God, and they shall be my people.
If the gospel were only about the death of Jesus and His resurrection, which is wonderful no doubt, but it would be powerless to have any affect on us, other than to be thankful for it. But God in His wisdom and wonderful providence and mercy, not only forgives us by the free gift of his grace, He also gives us power to transform us into a new creation! We become more and more like Jesus over time, if we continue in the faith.
And THAT my friend, is the GOOD NEWS!
Paul clearly states that anyone that continues to sin, Christian or not, will not inherit the Kingdom:
Know ye not that the unrighteous shall not inherit the kingdom of God? Be not deceived: neither fornicators, nor idolaters, nor adulterers, nor effeminate, nor abusers of themselves with mankind,
1 Corinthians 6:9,10
Nor thieves, nor covetous, nor drunkards, nor revilers, nor extortioners, shall inherit the kingdom of God.
That is the old, worldly way of living. We have to change, we can’t keep living like we used to:
And such were some of you: but ye are washed, but ye are sanctified, but ye are justified in the name of the Lord Jesus, and by the Spirit of our God.
1 Corinthians 6:11
There WILL be a Judgement. This is part of the everlasting gospel as well, and we will not have an excuse if we ignore it:
In the day when God shall judge the secrets of men by Jesus Christ according to my gospel.
Romans 2:16
For if we sin wilfully after that we have received the knowledge of the truth, there remaineth no more sacrifice for sins,
Hebrews 10:26,27
But a certain fearful looking for of judgment and fiery indignation, which shall devour the adversaries.
Wherefore, my beloved, as ye have always obeyed, not as in my presence only, but now much more in my absence, work out your own salvation with fear and trembling.
Philippians 2:12
But shewed first unto them of Damascus, and at Jerusalem, and throughout all the coasts of Judaea, and then to the Gentiles, that they should repent and turn to God, and do works meet for repentance.
Acts 26:20