Ostberg was the only challenger to eventual winner Ott Tanak last weekend, swapping the lead several times on Friday before the Toyota driver stormed clear through Saturday and Sunday as Ostberg struggled with tyre grip.
Having started just three rallies with Citroen in 2018, Ostberg recieved plenty of praise for his performance and hopes it will lead to a full-time contract.
"I would say this is the most important thing I have done in my life," he told Autosport.
Superior Tanak eases to Rally Finland victory
"I hope this is me back [in the WRC], it's been a long way back and I have done a lot of work behind the scenes.
"To be honest, 2016 was the lowest point and it turned around from there. I was happy with my '17 season, this showed me the level we compete at and gave me new respect for this sport.
Ostberg was without a factory drive in 2017 and instead ran his own team with a current generation World Rally car that proved economically unsustainable.
He then completed a deal with Citroen to compete in three rallies this year, but Kris Meeke's firing led to an extended season that takes in every event except Catalunya.
"Staying at home gave me that respect and it showed me how much this sport means to me," said Ostberg. "When you have something and it's gone, it really hurts and that made me fight to get it back.
"I had some opportunities, I used them and I'm really proud of that. It feels natural to be back with Citroen. Citroen feels like my home."
Citroen showed dramatic improvement in Finland, a year after it had been off the pace in what was a terrible maiden season for the C3 WRC that led to an overhaul that was completed last weekend.
Improved front geometry helped Ostberg's charge to second, but he added that his own set-up gave him greater confidence in the Citroen.
"I tried this [new geometry] for the first time before Sardinia and it made the front of the car much sharper," he said. This meant we could be soft [on the suspension], but we kept the reaction from the [front] axle.
"When the new rear geometry came [in Argentina] I didn't like it so much, because this gave more grip at the back of the car and you had to go softer at the front to cope with that, you lost that reaction.
"When we came to the Finland test, I told the team this was the best car I ever had for this rally.
"We came to Finland to fight for fourth place. We expected Toyota to be so far ahead. They tested for something like 20 days and we were here for three.
"It's amazing to be able to fight with them, I drove some of the best stages in my life in that fight with Jari-Matti [Latvala]."
Tanak takes step closer to Rally Finland win
Tanak holds narrow Finland lead over Ostberg
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