Operation Barbarossa called for the capture of Moscow within four months.
The Soviet Union did everything to prevent it. The Soviet forces conducted a strategic defense by constructing three defensive belts.
Moscow itself was also fortified. 250,000 women and teenagers worked building trenches and anti-tank moats around Moscow, moving almost three million m3 of earth with no mechanical help.
The Luftwaffe launched large-scale air raids on the city but those raids caused only limited damage because of extensive anti-aircraft defenses and effective civilian fire brigades.
And the last but not the least, the European Winter of 1941-1942 was the coldest of the twentieth century. The lowest December temperature reached –30 °C. The German troops were freezing with no winter clothing, using equipment that was not designed for such low temperatures. The Soviet troops were better prepared for this.