The text of the khutba is presented on FatemiDawat.com as translated by Shzd Dr Bazat Tahera Baisaheba (which was published in the context of her article on the art of oratory in classical Arabic literature.
In the khutba, Rasullulah explained that there are four things that we must do abundantly in Ramadan – two which will please Allah Ta’ala and two which you have no choice but to ask for. The two that please Allah Ta’ala are testifying that there is no God but Allah and seeking His forgiveness. The two that you have no choice but to ask Him for are praying for Jannatand seeking refuge from Hellfire. It is in light of this hidaayat of Rasulullah that our Hudaat Kiraamhave made it a custom to recite “allahumma haadha shahru Ramadan” after each farizat namaz, ending with the prayer “la ilaha illa allah, astaghfirullah, allahumma inni as’alukal jannah, wa a’uzu bika min an-naar” (see the English translation of this doa here).