President Trump will arrive in Brussels on the same day for a summit of North Atlantic Treaty Organisation leaders, where he is expected to reaffirm his commitment to the alliance and reiterate the need for member nations to meet the alliance's 2% defense spending recommendation.
The event, which is being jointly sponsored by the German Protestant Kirchentag and the Obama Foundation, will reunite Obama and Merkel, who maintained a close partnership and friendship when Obama was commander-in-chief, despite some tensions between the countries.
US President Donald Trump said that the attack was a response to the alleged chemical weapon use in Syria's Idlib province on Tuesday, which resulted in the death of over 80 people.
German Chancellor Angela Merkel is due to meet with world financial leaders in Berlin on Monday for talks that observers expect will focus on a growing trend toward protectionism.
The former US President will travel to Germany for the launch of a summer of special events to mark the 500th anniversary of the Protestant church.
Obama was in Berlin in mid-November on his last European trip as president.
"Together, as people of faith, we live from the firm hope for a better world", he added.
Obama has not kept quiet about his successor as some past presidents have done.
Gabriel told Tillerson last month that the North Atlantic Treaty Organisation demands would create a vast conventional German military that would be viewed with suspicion by European Union member states already fretting over Germany's leadership in economic matters. The churches form a global civil society network of over two billion Christians.
Just this past week, the Obamas were seen swimming and paddleboarding in the pristine waters of the South Pacific in French Polynesia.
Trump's first official visit to Germany is expected in July, where he will attend a meeting of G20 leaders in Hamburg.
Trump's visit will give him an opportunity to press his case for why many North Atlantic Treaty Organisation allies need to boost defense spending to help spread the cost of the security umbrella.