William Tyndale writes in his essay called "A Pathway into the Holy Scripture", this powerful definition of the Gospel. (This is found in Volume 1 of the Works of William Tyndale, published by the Banner of Truth, p 8).
“Evangelion (that we call the gospel) is a Greek word; and signifies good, very, glad and joyful tidings, that makes a man heart glad, and makes him sing, dance and leap for joy; as when David killed Goliath the giant, came glad tidings unto the Jews, that their fearful and cruel enemy was slain, and they delivered out of all danger: for gladness whereof, they sung, danced and were joyful. In like manner is the Evangelion of God (which we call Gospel, and the New Testament) joyful tidings … ".
This is the "balm of Gilead" that is spoken of in Jeremiah 8:22. The Lord Jesus Christ is the great physician and we need this message of good news to be preached every Lord's Day to a lost and dying world.