The Grove-based outfit endured a difficult campaign last year, finishing ninth in the constructors' championship after scoring just five points.
But a switch to Mercedes power and a revamp of its technical structure under Pat Symonds appears to have helped lift fortunes.
And with new arrival Massa topping the Jerez testing times last week on the final day, he says there are nothing but positives about Williams' situation right now.
"This test gives more confidence for the drivers, for me, for Valtteri [Bottas] but also for the people," said Massa.
"I think the people are so happy.
"There's smiling on my face. But it's not just on my face. You can see people smiling inside - it includes the mechanics, and the engineers.
"I think that's very important for the working, for the confidence and for the progress inside the team."
Analysis: Williams 2014 car insights
Despite the positive start in Jerez, though, Massa is equally aware that no team has yet shown its true performance, and there remain plenty of challenges for everyone right now.
"There is definitely still a lot of work and a lot of days in front until the first race, so it's too early," said Massa.
"We cannot forget that this is only testing. And I think maybe that this testing is even more difficult to explain compared to last year because the rules were the same then, and now there's a big change.
"Anything can change, anything can change in a few days, but I'm happy with what I found inside the team. It's better than I expected.
"The team has very good people, very professional people. There are so many new faces and so many people inside the team that knows how to make an F1 car; and you can feel the improvement every time you go out.
"I think that is what makes me smile more because I have a competitive team to work with, and I think that's pretty nice."