Lenin had finally just returned to Russia on the night of April 3rd (16 April). His journey had taken him from Switzerland across Germany via the infamous sealed train, then by ship to Finland and by railroad to Petrograd. There were cheering crowds to meet Lenin when he arrived at the Finland train station in Petrograd; everyone was expecting big celebrations; but Lenin thought differently. He immediately launched into a vicious attack on the Bolshevik party in Russia (actually, there were not that many Bolsheviks in Russia at the time); he was especially critical of the editorial board of Pravda, which happened to include Stalin.
Lenin was furious that the party, following the lead of the Petrograd Soviet, had announced conditional support for the Provisional Government, which had formed after the abdication of Tsar Nicholas II and then his brother Michael. The Soviet was operating under the impression that this was the capitalist revolution that Marx had prescribed and that a period of capitalist development was going to take place before the inevitable socialist revolution would occur sometime in the future. Well, Lenin, borrowing some ideas from Trotsky, decided that the future was now!
Lenin accused those Bolsheviks who were supporting the Provisional Government of betraying the socialist revolution. The party was in turmoil, and numerous debates ensued over the proper political course to follow. Stalin, as a member of the editorial board of Pravda, was faced with a particularly difficult choice. After a protracted delay of more than a week (During which time, I guess, that you would have to say that Stalin was coolly calculating his chances), Stalin opted to back Lenin. Other Bolsheviks, such as Lev Kamenev, continued to oppose Lenin.
Lenin's theses were short, clear, to the point and decisive (bread, peace, land, soviet power). They clearly were reflective of the fact that they were to be repeated ad infinitum at gatherings and meetings of workers and soviet deputies throughout Petrograd in the weeks to follow in 1917.