I believe that the purest answer lies within what the word "euangelion" meant to the original, First Century hearers. It was a widely used term which had no religious connotations at the time, and was understood as the heralding of one of three things: The Birth of a King, The Triumph of a King over his enemies, and a Regime Change (New King/New Order).
Hence, when the early church used the word "Euangelion"/Gospel, it was understood that a new King had been born, that He had defeated His enemies, and that there was indeed a regime change when Jesus was officially coronated through the finished work of the cross. Making those claims about Jesus was a revolutionary declaration that "Jesus is King" (and Caesar is not).
It meant so much more than today's typical "Evangelical" message. While there are many components of "The Gospel", I believe that what I have described is the crux of the Gospel. Just as "Hail to the Chief" is used to herald a U.S. President, "Euangelion" was a word reserved specifically for the ruling Caesar (or his successor) of that day.
Peace & Love!
When people in First Century culture heard the words "Preach the Gospel" (kēryssō euaggelion..."Evangelize"), they immediately associated that with HERALDING A REGIME CHANGE.
"Evangelical" is pretty much a 21st Century misnomer when there is no mention of King Jesus, the progressive coming of His Kingdom...and His will being done...on earth as it is in heaven.
Is the Kingdom past, present, or future?
The answer is "Yes" to all three.
Life after death, and Life after Life after death (resurrected, glorified bodies on a fully renewed Earth) are understood as God's free gift to mankind once we discover Life/Jesus before death and understand that victory over death is included in His "progressively coming" Kingdom!
The official New Age was ushered in at Calvary!
21st Century Evangelicals are focused on getting to heaven, while God is focused on bringing heaven to earth...through His New Creation!