The Strategic situation till 1941 June 21
By that time Berlin-Rome cleared the obstacles with quick campaigns, and the Madrid-Stockholm-Ankara neutrality triangle supported the Axis's structures, the new theater opened for the clashes on the east.
In the region of the Dnieper-Seret-Vistula rivers there's a gullet area which narrows Europe. From there to both directions the continent opens up, which opens up careless armies pushing forward as a fan, breaking up their concentrated formations, and they can be countered by the defending party more easily.
In the Eastern part of the area, bout at the middle lays the Rokitno/Pinsk/Pripyat marshes (he called it Rokitno), which divides the theater in a way that both fronts can be treated and led separately. This also can be exploited or can prove as a pain in the ass.
This part goes hand in hand with what Suvorov wrote:
Along the Western edge the Soviet deployed the Red Army two echelons. The job of the first echelon was to achieve breakthrough and open ways up for the second echelon for an invasion. At the moment of the German attack however the second echelon was still embarked and in move to the front, probably in the gullet's Eastern areas.