"It was not easy to make a historical document (Constitution) which binds a country which has more than a dozen sects, more than 100 languages and more than 1700 dialects and people living in places with various beliefs," Modi said while delivering a valedictory address on the National Law Day at Vigyan Bhawan here.
The prime minister also remembered country's first President Rajendra Prasad on the occasion.
He said the Constitution was not just a book but also contains social philosophy.
"On this day, 68 years ago, we decided the direction in which our country will move, those rules and laws were given by the Constitution and it is a day to remember those people who formed these epic documents," he added.
Modi stressed that the three arms of the government - Legislature, Executive and Judiciary - needed to work together and move in the direction of New India.
"Unfortunately, so many years have passed; we have not been able to remove our internal weaknesses since independence. We need to think about it at all levels," he said.
He also said, "Baba Saheb (Ambedkar) said that Constitution is workable, flexible and has power to unite the nation in times of war and peace. He also said if a wrong was done, it will not be the fault of constitution but the institution which is making people abides by the constitution."
The prime minister appealed the nation to come together and work towards the strengthening of India.
"India is a young nation. To strengthen it, all the constitutional bodies will have to come together and work towards it," he added.
The National Law Day is marked on November 26. On this day, the Constituent Assembly agreed on the final draft of the constitution in 1949. (ANI)