Why is the gospel called, “the gospel of peace”?

The gospel is the death, burial, and resurrection of Jesus.

"Moreover, brethren, I declare unto you the gospel...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 15:1, 3-4 KJV

The Bible says it is through Jesus’ shedding His blood on the cross for our sins, that we have peace between us and Jesus. Our sins separated us from Jesus. His blood reconciled us back to Jesus.

"And, having made peace through the blood of his cross, by him to reconcile all things unto himself; by him, I say, whether they be things in earth, or things in heaven." - Colossians 1:20

We apply the blood of His cross to our life by obeying the gospel. We obey the gospel by repentance, baptism in Jesus name, and being filled with His Spirit.

This is why the gospel is called “the gospel of peace.” By the gospel, Jesus shed His blood for us; by obeying the gospel, we find peace with Jesus.

Peter preached the gospel on the Day of Pentecost. The people that heard him then asked, “What shall we do?”

"Then Peter said unto them, Repent, and be baptized every one of you in the name of Jesus Christ for the remission of sins, and ye shall receive the gift of the Holy Ghost." - Acts 2:38 KJV

Peter and Jesus’ followers were sent by Jesus to preach the gospel beginning on that Day of Pentecost. (Luke 24:46-49, Mark 16:15-16). Peter preached “the gospel of peace.”

"And how shall they preach, except they be sent? as it is written, How beautiful are the feet of them that preach the gospel of peace, and bring glad tidings of good things!" - Romans 10:15