The 32-year-old has talked of being more relaxed and able to enjoy racing more since the announcement he would leave Ferrari and insists he is highly-motivated to thrive with Williams.
Can Massa thrive at Williams?
"The most important thing is that Williams wants to have me," Massa told AUTOSPORT.
"That's a really good thing, to go to a team that wants to have you to lead so I'm really happy about that.
"I've been really happy with my job in the second part of the season, so I'm really looking forward to having a very good last two races for Ferrari.
"I'm motivated and ready to do a good job with Williams."
EXPERIENCE IMPORTANT FOR 2014 CHANGES
Massa believes his experience from eight seasons with Ferrari will be vital to Williams.
He expects the major rule changes for 2014, including the move to 1.6-litre V6 turbocharged engines, will give the team a chance to make a big step forward.
"I think I have a lot to give to Williams as I have a lot of experience from a long time with Ferrari," said Massa.
"I know I can do a lot, especially with the big rule changes that we are going to have.
"I'm really happy with my choice and really ready to work as hard as I can to help Williams, also being part of a very important growing up compared to the season they have had."
Massa's Williams deal is described as "multi-year", meaning he will remain with the team until at least the end of 2015.
He believes he still has a long future in Formula 1 and is hoping to establish himself at Williams for the longer term.
"That's what I'm looking for and ready for [a long-term Williams future]," said Massa.
"It's not just a one-year contract, it's more than that so I am very happy and ready to work as hard as I can."
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