This is the 638th most frequent Korean word.
본격적인
"본격적인" means "full-scale" or "in earnest."
In this sentence, '본격적인' describes '여름' to emphasize that summer is now in its peak and fully expressed state.
본격적인 여름이 시작되었다.
The full-fledged summer has begun.
In this context, '본격적인' indicates that the preparations should be complete and carried out in earnest.
본격적인 준비를 시작해야 합니다.
We need to start the full-scale preparations.
Here, '본격적인' is used to highlight the sincerity and intensity that should characterize the discussion.