There's basically two reasons for the invasion of the Soviet Union in June 1941

• Hitler ideologically wanted the land of the Soviet Union for the German people and
• while it was a stalemate between the UK and Germany in 1941, in the medium term the much bigger British Empire, assisted by the US's vast economic and industrial resources, would be able to grind Germany down.

The Germans had a brief window in 1941, before the UK returned to active war in Europe, when their Wehrmacht could go East, defeat the Soviet Union and use the resources there to produce the tanks and aeroplanes to defend the West from invasion / defeat the UK.

To unpack that a bit, ideologically the Nazis believed that all races were in competition and that the weakest would perish. Due to lower birth rates in Germany (especially urban Germany) compared with Slavic nations in the East, the Nazi fear was that in time the German people would be outbred and swamped by Slavs. The solution was to take the Slavic lands in the East and give them to Germans. From this we get two phrases

Drang nach Osten - Drive to the East and Lebensraum - Living Space (for the German race) which describe this ideology.

It seems that Hitler was inspired somewhat by the example of the British Empire in India (small groups administrators exploiting millions) and the US which, from Hitler's POV, expanded from 13 colonies into an industrialised continental empire ran along racial lines.

While Lebensraum explains the Nazi desire to go East it doesn't address why it was though necessary to do it in 1941 with the British Empire still in the war especially when the Germans knew the perils of a two front war.

Firstly it has to be recognised that Nazi Germany was economically relatively weak compared with the British Empire, France and the US. In real terms that meant that in a war, those countries could produce more tanks, more aeroplanes, more artillery pieces, artillery shells, ships etc. They would also have more resources for R&D allowing the production of increasingly sophisticated armaments.

In Adam Tooze's The Wages of Destruction he argues (convincingly to me) the Germans were well aware of the economic disparity that would inevitably tell in the long term and the logically response for Germany was to go to war as soon as possible and use every resource that it had regardless of the future.

In 1940 that approach defeated the French and British armies in France but due to the overwhelming size of the Royal Navy and Airforce the Germans could never conquer the Britain.

As Britain would not make peace, Germany was faced with a choice turtle in Europe and hope to defeat a future British invasion (backed by US aeroplanes and tanks which were being produced by the thousand) or risk it all on the invasion and capture of the Soviet Union in one summer.

Turtling in Europe might seem like the sensible idea but the Nazi empire, despite having much of the continent under control, was woefully inefficient in producing war equipment and was lacked sufficient agricultural produce and coal, iron, other metal ores and oil needed to match industrial output in the US.

All of that economic promise lay in the west Soviet Union. The temptation for Hitler in 1941 was then to solve all his problems in one campaign. He'd capture Lebensraum, the economic capacity of the western Soviet Union and then be able to fortify the West or create an airforce and navy to defeat Britain.