In a speech that drew a standing ovation from delegates to a special party congress in honour of the unification anniversary including Chancellor Angela Merkel, Kohl said Germany must now muster strength for new challenges.
"Dear friends, these dates are an occasion to take pleasure in what we have achieved, to remember with gratitude and pride who we are and from where we have come, and also to look forward together," Kohl said.
Kohl, now 80 and confined to a wheelchair, presided over the fall of the Berlin Wall on November 9, 1989, and the merger of East and West Germany on October 3, 1990. He is known here as the father of German unity.
His speech slurred by a litany of health problems in recent months, Kohl warned that climate change, European integration and the inclusion of immigrants in German society could only be tackled with conservative solutions.
Days after the government unveiled what it called a highly ambitious energy plan to cut emissions and promote renewable energy, Kohl cautioned that Germany would suffer economically if it tried to go it alone.
"There is no sense in pursuing sensible national policy if we do not have any international allies," he said.
Kohl, who served 16 years as chancellor, said that the dreams of greater European unity after the fall of the Wall must not be lost in the wake of the eurozone debt crisis.
And following an incendiary new book by a central banker who was forced to resign for arguing that the country was being made "more stupid" by unproductive Muslim immigrants, Kohl called for a frank debate on the issue.
"We must not limit our discussion about education and integration to immigration," he said. "To the contrary, the time has come to have a discussion about our own identity," with an emphasis on the values that led to West Germany's post-war "economic miracle."
Kohl offered the embattled Merkel, who has watched her Christian Democratic Union plummet in opinion polls since her election to a second term last September, a few warm words of encouragement.
"Don't listen when people say that our voter potential is dwindling – the people are our potential, it is up to us to win them over," he said.
The 56-year-old Merkel, who grew up in communist East Germany, thanked her former mentor Kohl for his contribution to German unity.
"You showed fortitude when others faltered," she said. "You never stopped highlighting the injustice of the GDR (East Germany) with our neighbours abroad and pushing for the right of our country to unite while others just wanted to accept our division."
In a poll released Friday, 84 percent of Germans said they believed national unification after four decades of division had been the right decision, despite a lingering economic gap between east and west.
Just 14 percent said unity had been a mistake, according to the survey for ZDF public television.