Tā de guāndiǎn hěnduō, yīyányǐbìzhī, jiùshì fǎnduì gǎigé.
He made many points; to sum up, he opposes the reform.
Tips
history
Directly from 论语·为政: 诗三百，一言以蔽之，曰'思无邪' - Confucius boils down all 300 poems of the Shijing into a single phrase (思无邪, 'thoughts without depravity'). The idiom has been used for the same rhetorical move ever since.
register
Formal and literary. Sentence-initial: 一言以蔽之，... introduces the summary. In casual speech, 总而言之 or 简而言之 are more common equivalents.
