Singapore needs to forge a common identity among its people, so that the country can hold itself together and succeed.
This bond is needed because as Singapore progresses, there is the danger of becoming so globalised that there is no distinctive identity that sets Singaporeans apart from non-Singaporeans.
"If we become so comfortable abroad that we lose the sense that only Singapore is truly home... if a large part of our talent goes overseas seeking challenges or fortunes, then I think we will be depleted, our centre will not hold... we will just melt away, dissolved by globalisation."
On the flip side, Singapore could be divided along the lines of race, religion and values.
But a unity and common identity can arise when people share values - such as meritocracy, multi-racialism and fairness and justice in society. These bonds are born when they share experiences such as going to schools and national service together, or celebrating successes like the SEA Games.
Overcoming crises such as the outbreak of Sars in 2013, or grieving together at the death of founding Prime Minister Lee Kuan Yew, or in the face of tragedies like the deaths of schoolchildren and teachers on Mount Kinabalu last month, also brings people together, said PM Lee.
There will be hard times in the 50 years ahead, but these tests will also be an opportunity for Singaporeans to bond, he said.