Hitler wanted to invade the UK as it was, at the time, the only country still fighting against him. His planned invasion required the knocking out of the RAF and that is what was tried in late August/September 1940 and is now known as The Battle of Britain. Had that gone on for much longer, it is doubtful whether the RAF could have survived. However, suddenly and for no apparent reason, the Luftwaffe turned from bombing RAF facilities to bombing cities, first London and then others. This became known as the Blitz. This enabled the RAF to regroup and rearm.