Why, Seek first to grok then to be groked?

Because if you don't grok the vernacular/language your target audience uses, then you can't make yourself and your message comprehensible to them, which means you can't influence or lead them.

However, if you seek first to grok, then to be groked, then you will acquire your target audience language and vernacular, you can channel your desired message to them using their words, then they are far more likely to comprehend your message and intent, and be influenced.

Which dramatically increase the probability you will achieve your desired outcome.