EVANGELION (GREEK) Literally... WELL MESSAGE it denotes the good tidings of the grace of God toward mankind. John 3:16.
The Messiah, Jesus came to fulfil the promises and the Law given to Israel, God's chosen people. Matthew 5:17. He also brought in a new dispensation.

God has readjusted the ages to suit the conditions, Hebrews 11:3. brought about by the apostasy of Israel, who were under the Law given through Moses. John 1:17.
But the flesh was weak in its attempt to keep the Law. Romans 8:3
In this new dispensation of God's grace, He has dealt with the sin problem, through the offering of His Son Jesus. Romans 5:8. "Faithful is the saying, and worthy of all welcome, that Christ Jesus came into the world to save sinners" 1 Timothy 1:14,15. Gk.

Now mankind is not under the Law, but under God's grace. Romans 6:14,15. It is not working for salvation but believing God's word that He has dealt with our sin problem. Romans 10:8,9 Amplified.

"The word (God's message in Christ) is near you, on your lips and in your heart; that is, the Word - the message, the basis and object - of faith, which we preach. Because IF you acknowledge and confess with your lips that Jesus is Lord and in your heart BELIEVE (adhere to, trust in and rely on the truth) that God raised Him from the dead, you WILL BE SAVED".

Then look at Romans 10;13

"For everyone who CALLS upon the name of the Lord (invoking Him as Lord) will be saved"

KATALLASSO. Gk. Literally means -down-change, conciliate, one side only, in an estrangement, to make friends.

Sin no longer bars us from the presence of God. Justification is the ground of peace. Yet peace is a favour infinitely beyond justification. God's affections are not satisfied with clearing us from all guilt, He craves our love and adoration. Righteousness alone does not give us a passport into His presence, but this further grace of reconciliation urges us into full and affectionate fellowship with Him. We have the living Son of God as a surety of our salvation. We shall be saved by His life. Romans 5:1-11. Gk

"For if, being enemies. We were conciliated to God through the death of His Son, much rather being conciliated, we shall be saved IN His life. Yet not only so, but we ARE glorying IN God, through our Lord, Jesus Christ, through whom we NOW obtain the conciliation." Faith

It is the belief in the statement of another. Faith is the main factor in this Dispensation of Grace concerning the evangel.

The good news, the gospel, the evangel is not concerning the sinner but concerning God's Son. Paul was commissioned by God to reveal this good news to the nations. Acts 9:15,16.

"Paul, a slave of Christ Jesus, the called apostle, having been severed for God's evangel (good news) concerning His Son Jesus Christ our Lord". Romans 1:1-7. Gk.

Salvation, in its beginning, is of faith in order to accord with grace. Faith is the simplest, easiest, freest channel God could choose to convey His righteousness to mankind. Romans 4:16.

In Ephesians we have the further truth that such a salvation - through faith -- calls us for further favour in the future. Ephesians 2:8 Then in Romans 1:16,17 Amplified.

" For I, Paul, am not ashamed of the evangel, good news, of Christ; for it is God's power working unto salvation to everyone who believes with a personal trust and a confident surrender and firm reliance."