Hadith 18 of an-Nawawi enjoins believers to have piety and work righteously.
Piety refers to being conscious of God and seeking to do what is right in accordance with His guidance. It involves having a deep sense of reverence and awe towards God, and striving to live in a way that is pleasing to Him. Righteousness, on the other hand, refers to acting in accordance with God's commandments and doing good deeds.
So, this Hadith teaches us that as believers, we should strive to have piety and work righteously in all aspects of our lives. This means being mindful of God in everything we do, whether it's in our personal relationships, our work or studies, or our social and community activities. It also means striving to do good deeds and to be of service to others, in line with the teachings of Islam.
By following this Hadith, believers can become better individuals, and contribute positively to their communities, promoting peace, justice, and compassion.