Keep your promises/vows

In this hadith, the Prophet Muhammad is advising Umar to fulfill a vow he had taken during the days of Ignorance, or pre-Islamic period. This shows us that even if something was done before one accepted Islam, it is still important to keep one's word and fulfill their promises and vows made in the past. It also teaches us that we should be honest and trustworthy in all our dealings with others, no matter what religion they may follow or what time period they are from. This hadith also emphasizes the importance of keeping our promises and being true to our word as Muslims, which is an important part of Islamic teachings.