Opposite of the word 'rigid'

The word which is nearest in meaning to the word 'profound'? 

The bundle is so heavy that I cannot lift it

(Use 'too' instead of `so   that') 

Rahul is very rich. He can buy a car (Combine using 'enough')

The appropriate meaning of 'run-of-the-mill'

Within a short period of time, he reached the ____ of his career