A proverb meaning you should follow the customs and rules of the place or group you are in (equivalent to 'When in Rome, do as the Romans do').
海外で生活するなら、郷に入らば郷に従えという気持ちが大切だ。
When living abroad, it's important to adopt the attitude of 'When in Rome, do as the Romans do.'
新しい職場ではまず郷に入らば郷に従えと思って振る舞った。
At the new workplace, I behaved with the mindset of 'When in Rome, do as the Romans do.'