Metsola, who has been visiting Poland since Thursday, met Prime Minister Donald Tusk and President Karol Nawrocki.
On Friday she held talks with the Speaker of the Sejm, lower house, Włodzimierz Czarzasty, before addressing Polish MPs.
"My generation knows what a Europe with and without the European Union looks like," she said.
"We are far from perfect, we must be open to reform, to change, to fix what is needed. But ultimately, a world with the European Union is is a better place for all of us."
She pointed out that Poland’s economy had grown twice as fast as the European average since it joined the bloc and was now among the world’s 20 largest.
"You will soon take your place at the G20 table," she said, adding that she hoped it would be a permanent one.
"People call it the Polish miracle, but this was about hard work."
Security was another major theme of her speech.
Metsola said Poland had long warned Europe about Russia, energy dependence and what the Kremlin was capable of, but "too many in Europe did not listen."
"You were right."
She noted that Poland’s EU presidency had made security a priority and that the country had been the first to show why European defence funding mattered.
The country knew what it meant to stand on the front line, she said, pointing to Russia’s invasion of Ukraine, Belarus’s exploitation of migration and acts of sabotage.
"When Poland's security is tested, Europe's security is tested," she stressed.
Europe would never forget that Poland had opened its doors to refugees from Ukraine.
Metsola also said the EU was not about everyone being the same.
"This project of ours is not about any imposition from Brussels," she said, but about acting together and making decisions which are "closest to the people they impact the most."
"If there are things to change, let's do that together. Europe is you, not anyone else," she emphasised.
During her speech, MPs from the opposition Law and Justice (PiS) party held up placards in English saying a "coup d’état" was under way in Poland, launched by Tusk.
Others showed photographs of police outside the Constitutional Tribunal, and one sign read "Tusk = dictator."
The prime minister posted a photo from the chamber on X showing the banner behind him.
Asked about the protest over Poland's constitutional court, Metsola replied that all she would say was that it was "democracy."
She added that she had spoken in the parliaments of all EU countries and beyond, and it was good to see a lively, democratic debate.
(ał)
Source: PAP