The election results have given the People's Action Party (PAP) "precious political capital" that it must make good use of, wisely, Prime Minister Lee Hsien Loong said.
In a speech to newly elected PAP MPs, which he traditionally gives soon after a general election (GE), Mr Lee said the Government will have to take hard decisions from time to time.
When it does, he told MPs they must justify them to the people and win their support to maintain trust and confidence in the PAP.
His comments on what MPs need to do, how they should behave and the significance of the landslide victory were made in the Parliament building on Monday behind closed doors. An excerpt was posted on Mr Lee's Facebook page yesterday.
Parliament will open in January, Mr Lee said, urging the MPs to think about what they want to say in their maiden speeches.
STAYING HUMBLE IN VICTORY
In victory, we must be humble, and stay close to the people whom we serve. The PAP must never become arrogant - whether in the personal behaviour and attitudes of MPs and activists, or in the policies and actions of the party and Government.
PRIME MINISTER LEE HSIEN LOONG, on the need for MPs to work even harder
"We may all wear white, but each of us brings a different experience and perspective. Each strengthens the party in a different way, with different groups in our society."
Mr Lee said it was healthy for the PAP that every seat was contested, as this strengthened the party's fighting spirit and fighting skills.
"We must not assume that the next election will be easy," he said. "We must keep on working to persuade new voters of our ideals and convictions, and keep on updating our party and programmes to stay in touch with voters."
He said the Government will name and swear in the new Cabinet in a fortnight's time. His emphasis is on pushing leadership renewal, with younger ministers given positions of heavier responsibility.
The results, he said, were "better than we had dared to hope; indeed better than anyone expected".
PAP MPs on the ground and government agencies "put in much hard work over the last four years, and longer", he said.
"But election outcomes are never fully predictable, and we must never take anything for granted."
The PAP won 83 out of 89 seats in the Sept 11 GE, and got 69.9 per cent of the popular vote - a 9.8 percentage point swing from GE2011's 60.1 per cent, its lowest since 1963.
The PAP also regained Punggol East SMC, which the Workers' Party (WP) won in a 2013 by-election. The WP retained Hougang SMC and Aljunied GRC with reduced margins.
"Politics always requires a stout heart, wherever the contest may be. But the stoutest-hearted were our candidates who stood in the opposition wards and did very well," Mr Lee said.
He thanked retiring MPs whose "patient efforts tending the soil in years gone by have yielded the fruit we harvested this GE".
GE2015, he said, was an "important success" not only for the PAP, but also for Singapore and Singaporeans. "Since GE2011, investors overseas have been asking if Singapore is still open for business. A weak result this time would have affected their confidence," he said.
"Instead, GE2015 has boosted confidence in Singapore. This will create more opportunities for our people, despite a challenging regional and international environment."
The strong result also ensures Singapore's leadership renewal is given "the best chance to succeed".
"We have more good people whom we can groom and expose early, to enable us to build the strongest team to serve Singapore."
Mr Lee reminded MPs to "work even harder for Singaporeans".
"In victory, we must be humble, and stay close to the people whom we serve. The PAP must never become arrogant," he added.
MPs should also lose no time going to the ground, engaging residents and building support, he said.
"Winning GE2021 starts now.
"Together, we will work with Singaporeans to put the country on a strong start towards SG100."