Davies twice pulled the Revolution back level against New York Red Bulls as New England triumphed 4-3 on aggregate to reach the MLS decider against either Los Angeles Galaxy or Seattle Sounders.
The 28-year-old striker, who almost died in a car accident five years ago, struck with two headers at Gillette Stadium, converting from a corner in the 41st minute and then scoring again with 20 minutes left from Chris Tierney's cross.
It was Davies' second brace in the MLS Cup play-offs this season.
"For me, personally, it's unimaginable really," Davies told the MLS website.
"These five years, really just grinding it out, things would go against me and there's a lot of tears and pain. Through it all I just continued to fight and stay with it and things have turned out for the best."
Davies paid tribute to his Revolution team-mates and the club's staff for believing in him and helping him return to regular football since he joined the club last season.
"I think what's really important, the guys in this locker room have pushed me since I've been here," he said.
"They've really seen the potential that I have and they want me to succeed and that goes a long way. That's why I'm playing the way I am now."
But Revolution coach Jay Heaps would have none of it.
"I credit Charlie on all of it," the 38-year-old said.
"We gave him a stable environment but he was fighting for his position every day, from when his injury happened to the entire 2014."
New England will now look to end their MLS Cup drought, which has seen them fall at the final hurdle on four occasions previously.
"To be in my first MLS Cup - and this franchise has been there three or four times and hasn't won yet - for us to finally win one would be extremely special, especially because I grew up here," Davies said.
"Bringing a championship back to Boston would be the ultimate goal and something that we hope we can do."
