Will try to put it terms you may understand:

One does not have to be qualified (accroding to your standards) to enlist in the army.

The army does absolutely recruit unqualified individals aka high school students (mainly men) with a pulse.

To be a leader in the army, you do not have to have made some breakthrough invention. It does not matter if you came from wealth or if you were born poor.

To move up in the army ranks, you have to commit yourself to service and do the job.

In the years since Greta has come onto the climate scene and cause, she has committed herself to service and to the job.

Sorry you just don't like her - she can be a bit scary at times ;)