This is the 942nd most frequent Japanese word.
べ
A particle indicating speculation, intention, or suggestion; often dialectal.
べき is used here to express an action or situation that is recommended or an obligation.
行くべきことだ。
It is something that should be done.
べ (in よければ) serves as part of a conditional form, indicating 'if' for the condition.
天気がよければ海に行こう。
If the weather is good, let's go to the sea.
べる is derived here from 遊べる, meaning 'can play', indicating the potential form of the verb.