What is the " Good News " ?

The word 'Gospel', in the Greek (the original language of the New Testament ) means 'Good News'.
The apostle Paul wrote much concerning the Gospel.

Romans 1:15-17
15 “That is why I am so eager to preach the gospel also to you who are in Rome.
 16 I am not ashamed of the gospel, because it is THE POWER OF GOD FOR SALVATION to everyone who believes, first to the Jew, then to the Greek. 
17 For the gospel reveals the righteousness of God that comes by faith from start to finish, just as it is written: “The righteous will live by faith.”…

(In the Greek, the word translated ‘power’ comes from an English transliterated, root word,’ dunamis’, from which we get the word ‘dynamite’. From that implication we can see the significance of the Gospel’s ‘change effects’ in one’s life.)

Paul defines the 'Gospel' for us in I Corinthians 15:1-4:
"By this Gospel you are saved, if you hold firmly to the word I preached to you.... For what I received I passed on to you as of first importance: that Christ DIED for our sins according to the Scriptures, that He was BURIED, that He was RAISED on the third day according to the Scriptures (1 Corinthians 15:2-4).

Skip down to I Corinthians 15:12 – 19. Here we see just how totally important the Gospel, i.e. Jesus’ death, burial and resurrection, is to our eternal souls:
12 “Now if Christ is preached, that He has been raised from the dead, how do some among you say that there is no resurrection of the dead? 
13 But if there is no resurrection of the dead, not even Christ has been raised;
 14 and if Christ has not been raised, then our preaching is vain, your faith also is vain.
 15 Moreover we are even found to be false witnesses of God, because we testified against God that He raised Christ, whom He did not raise, if in fact the dead are not raised.
 16 For if the dead are not raised, not even Christ has been raised; 
17 and if Christ has not been raised, your faith is worthless; you are still in your sins.
 18 Then those also who have fallen asleep in Christ have perished.
 19 If we have hoped in Christ in this life only, we are of all men most to be pitied.”

In essence the apostle Paul said that if Jesus has not risen from the dead, everything taught in the name of Jesus is worthless, our faith is void, and we are still in our sins.
 That’s how significant it is that Jesus, the Son of God, came from heaven to earth, lived and died a sinless man, that we can be given His holiness as He took on our sins and took our punishment, on the cross…..and then arose victorious over death in the likeness of which we will one day be raised up if we are children of God with God’s Holy Spirit living in us. (Romans 8:11)

Jesus said to her, "I am the Resurrection and the Life. He who believes in Me will live, even though he dies; and whoever lives and believes in Me will never die. Do you believe this?" (John 11:25-26).

Question: Do we believe?

If someone is sitting inside their home and hears the warning ‘FIRE!’ , ‘FIRE’, and takes no action, it would seem obvious that they ‘heard’ but did not believe. On the other hand, the person who hears and then grabs their children, pets etc. and gets outside the structure, clearly heard and believed. The point being that genuine faith (beyond 'mental ascent') acts upon the truth that's been received. The book of James teaches considerably about proving ones faith in action.

I do not think that it is without significance that the scriptures make a point, in Acts 2, of distinguishing those who ‘gladly received the word and were baptized, 3000’, and those who did not take action.

In light of Paul’s definition of the ‘Gospel’, I Corinthians 15:1-4……Question - How can the death, burial and resurrection of Jesus (the Gospel according to Paul) be Good News?

Simply put, without Jesus' death on the cross, AND His resurrection that proved He was no ordinary man but rather that He had the power over death,(the Son of God), we could not be saved from our sins.

Scriptures teach that Jesus took our sins on Himself and that He suffered the punishment that we deserve so that we do not have to perish.

I Peter 2:24
"...and He Himself bore our sins in His body on the cross, so that we might die to sin and live to righteousness; for by His wounds you were healed."
In rising from the dead Jesus proved His power over sin and physical death...Satan's two claims to the lives and souls of mankind.

I Corinthians 15:56-57
"The sting of death is sin, and the power of sin is the law; 57 but thanks be to God, who gives us the victory through our Lord Jesus Christ."

Hebrews 2:14
"Since the children have flesh and blood, he too shared in their humanity so that by his death he might break the power of him who holds the power of death--that is, the devil--"

1 John 5:4
"...for everyone born of God overcomes the world. This is the victory that has overcome the world, even our faith."

II Corinthians 5:21
"He made Him who knew no sin to be sin on our behalf, so that we might become the righteousness of God in Him."

Romans 3:25
"God presented Christ as a sacrifice of atonement, through the shedding of his blood--to be received by faith. He did this to demonstrate his righteousness, because in his forbearance he had left the sins committed beforehand unpunished--"

Romans 4:25
"He was delivered over to death for our sins and was raised to life for our justification."
Note that repentance precedes baptism, just as faith precedes repentance and baptism. John the Baptizer was a prophet who prepared people to accept Jesus.
 He did this by "preaching a baptism of repentance FOR THE REMISSION OF SINS." (Mark 1:4). "Repentance" refers to the decision to change, to stop living in sin and start following Christ. Baptism marks that change with this purpose: "for the forgiveness of sins."

When the repentant believer is immersed into Christ for the remission of sins, they arise from the waters free of the ball and chain of sin and with the gift of God's Holy Spirit.

THAT's why the Ethiopian went on his way 'rejoicing'!
And we can too!
THAT is Good News!   Amen!