The letter comes amid uncertainty over the new EU budget caused by a dispute between Brussels and some EU states over attempts to link funding to the maintenance of the rule of law.
The Polish government, which has been accused of undermining the rule of law, has threatened to veto the budget, arguing that linking funding to behaviour would break EU regulations, and could lead to countries losing funding for subjective political reasons.
In his letter the president seemed to reflect the government’s position.
"We want to work for the implementation of an ambitious EU budget and the EU Recovery Plan," he wrote.
"The EU has always been defined as a community of law and must remain as such," the Polish head of state said, adding that "no reforms, no principles of operation and no EU policies could either exceed treaty norms or be interpreted freely."
President Duda went on to say that the work and effectiveness of Polish diplomats in the international arena were of particular importance since Poland's membership in the EU - perceived as a community of equal states and free nations - was of key significance to Poland's economic development.
He added that “Poland’s voice must be heard” when it came to dealing with the effects of the pandemic on the continent, and any rebuilding that needed to be done once the pandemic had finished.
With this in mind Duda said Polish diplomats would back the development of European mechanisms supporting health and joint research in biotechnology and therapies.
He also said that, in order to overcome the economic effects of the pandemic, it was necessary to come up with measures designed to shorten supply chains and strengthen Europe's technological and industrial independence.
"Europe should again become a modern 'production workshop' while the profits should be distributed in an honest way, by means of linking cohesion and development goals," the president said.
Duda also wrote that Poland had not forgotten about its eastern neighbourhood and was consistently reminding the EU of its existence.
Poland, he said, supported both the Belarusian people in their struggle to freely express their political will, and Ukraine's territorial integrity. He also opposed Russia's politics of imperial interference, its breaking of laws and not respecting human rights. (PAP)