If "the Gospel" is the announcement that God has made a way for us to be righteous apart from good works, then why does Luke start his gospel by telling his readers about Zachariah and Elizabeth who were
"both righteous in the sight of God, walking blamelessly in all the commandments and requirements of The Lord"? (Luke 1:6 NASB).
It would seem that Zachariah and Elizabeth already possessed the blessings of such a gospel, being "righteous" and "blameless". If they already had these things, then why did Jesus come at all?
The point of observing the mosaic Law (the Torah) was never done with the objective of earning one's passage into heaven. The goal for the Israelite, or rather, God's goal through the Israelite, was never to get people to Heaven. The goal was the reclaiming and renewing of the entire cosmos that God had created, declared as "good", and was grieved over because of the sinfulness of the human image bearers (humans) who had committed great evil in it. God had made a promise to Abraham and his family that they were going to be his agents of new creation (Genesis 12:3). The Torah was the covenant charter of this arrangement. Observing the statues of the Torah did not earn you free passage into a blissful after-life. Observing the Torah was an outward sign that you were in covenant with the Creator God and you were actively conscience of that covenant. This active consciousness declared that you were in right standing concerning the covenant that God made between Himself and Abraham's family. I.E. You were "righteous" in regard to the covenant. This doesn't mean that Zachariah and Elizabeth were without sin. It meant that they were people prepared, ready and waiting, to benefit from what God was finally about to do in and through Israel and for the whole world. These would be some of the people "on whom God's favor rests" (Luke 2:14) as the angels would describe to the shepherds on the night Jesus was born. The fact is, Jesus didn't come to give us a free ticket to heaven. Jesus came to establish the rule of Heaven on earth with the assurance of the resurrection of all the righteous dead who will one day awake, not in heaven, but on earth to enjoy the entirely renewed cosmos! That is why the Gospel is good new for the entire planet earth!