I believe that Hitler's main aim was to attack the Soviet Union. It wasn't just a rash decision. He wanted to carve out a whole section of the Soviet Union and add it permanently to the Third Reich. He wanted land and natural resources. He also wanted to destroy  Bolshevism. There never would have been a better time to invade the Soviet Union than when he did. He tried to neutralize Great Britain by offering a peace treaty so that he would only have to worry about the Eastern Front. But Churchill rejected any such treaty and warned Stalin that Hitler planned to invade the USSR. Then Hitler tried to bomb Britain into submission, but that didn't work, and it cost him valuable time. If he had waited for some years to invade the USSR, or if he had never invaded, the USSR and International Communism would have become a greater and greater threat. Stalin might have ended up invading Germany, rather than vice versa. The Germans were astonished at the ability of the Soviets to produce modern tanks, planes and heavy artillery in great quantities.

I agree.  Russia has proved to be too large and too cold for many conquerors.  The Nazis's should never have targeted Russia.  It simply stretched their troops and resources too thin.  Perhaps in a war between Germany and Russia, they might have succeeded, but Russia was not the only ground the Germans had to hold.  Russia was able to concentrate their efforts on holding off the Germans while the Germans were fighting many battles besides just the invasion of the Soviet Union.  In essence, they bit off more than they could chew.  It allowed the other battle fronts to be weakened the opposition was able to gain ground.

I agree, and invading Russia has historically proven to be bad mojo.  It did not work out well for Napoleon or for the Central Powers in WWI.  It was a costly mistake for the Axis that changed the course of the war in favor of the Allies.  The Nazis should have payed more attention to their history teachers...

Post #2 is correct. I would also add that initially, it looked like the German invasion of Russia was going to be successful. The Russians were pushed well back past their boundaries. Then the Russian winter set in and slowed the Germans down, giving the Russians time to regroup and re-arm and counterattack.

This is because the Eastern Front ended up using up huge numbers of German soldiers and huge amounts of German equipment.  Russia was simply too large of a place with too many soldiers and too much equipment for the Germans to succeed in their attack.  When they failed, it led to the loss of huge amounts of military strength.