There's two straightforward and entirely justifiable reasons for his speech.
1.) As president of the European Council, it's his job
Here is a direct quote from the European Council's website as to what their role is:
The European Council is one of the 7 EU institutions. However, it is not one of the EU's legislating bodies, so does not negotiate or adopt EU laws. Instead its main role is to determine the EU's general political direction and priorities - essentially setting the policy agenda for the EU.
Traditionally, this is done by adopting conclusions during each European Council meeting. These conclusions identify specific issues of concern for the EU and outline particular actions to take or goals to reach. European Council conclusions can also set a deadline for reaching agreement on a particular item or for the presentation of legislative proposal. In this way, the European Council is able to influence and guide the EU's policy agenda.
In addition to this, here are the five priorities of the European Council
* Jobs, growth and competitiveness
* Empowering and protecting citizens
* Energy and climate policies
* Freedom, society and justice
* The EU as a strong global actor
Britait clearly falls within this remit - to be specific the first and second bulletpoint on the list, which are now tangled up into one large bundle as a result of Amber Rudd causing all manner of Godwin's Law violations when she proposed employment guidelines straight out of Mein Kampf. When there's a swivel-eyed loon saying that qualified EU nationals should be overlooked for jobs they are qualified for because their parents happened to have sex on the opposite side of the channel, decreasing the amount of jobs and increasing unemployment based on the accident of birth, that's something for the European Council to address - especially when Theresa May is acting as if the UK can still trade with the EU as if everything is the same as it always was.
ii.) It is the role of the European Policy Centre, who he was addressing
Here's the EPC's mission statement, taking from their website
The European Policy Centre (EPC) is an independent, not-for-profit think tank dedicated to fostering European integration through analysis and debate, supporting and challenging European decision-makers at all levels to make informed decisions based on evidence and analysis, and providing a platform for engaging partners, stakeholders and citizens in EU policy-making and in the debate about the future of Europe.
Similarly, here are the priorities of the EPC
* Independence and transparency
* Excellence, relevance and innovation
* Cross-cutting and long-term solutions
* Multi-constituency and inclusive
* Partnerships
What is the subject that requires the higher-ups to make an informed decision or six, which requires a long-term solution to benefit all parties? Britait.
There's no agenda, it's someone doing their job - sort of like Poch talking about West Brom in his press conferences this week.