But why did Allah give Luqman the ability of wisdom? He was not given wisdom because of wealth, children, lineage, or given habits, but it was because he was self-restrained, taciturn and also a deep thinker. Additionally, he was never seen spitting, clearing his throat, squeezing the lemon, answering the call of nature, bathing, observing trivialities, or foolishly laughing. He was very eloquent and he had good manners, and he was not arrogant. He did not weep or cry when any of his children died either. Luqman would also frequent the rulers and governmental officials to mediate and think thoroughly and find admonition. Because of all of these factors, Allah granted His servant with great wisdom.
Luqman was a great role model to his children, and Allah says in the Holy Qur'an that he would often advise his son. Luqman once told his son, “O my son! Join not in worship others with Allah. Verily, joining others in worship with Allah is a great Zulm (wrong) indeed!” (31:13) This means that to associate partners with Allah falls under the heading of shirk. Such things were done by the people of Fir'aun and the Samiri who came many years before him. Luqman also says to his son, “O my son! If it be anything equal to the weight of a grain of mustard seed, and though it be in a rock, or in the heavens or in the earth, Allah will bring it forth. Verily, Allah is Subtle in bringing out that grain, Well-Aware of its place!” (31:13) Luqman here is forbidding his son to do wrong to the people even in the slightest way, for Allah will bring it forth and bring him to account on Yawm al-Qiyamah.
Luqman further advises his son, saying, “O my son! Perform your Salah properly, then enjoin on people Al-Ma'ruf (Tawheed and all that is good), and forbid people from Al-Munkar (disbelief in the Oneness of Allah, polytheists of all kinds and all that is evil and bad). Endure patiently whatever shall befall you.” (31:17) He is telling his son to perform Salah properly and on time, and then he tells his son to enjoin the good and forbid the evil, before he concludes this advice, telling him to be patient in whatever challenge he may face while doing this. Then Luqman says, “And do not turn your nose up to people, nor walk pridefully upon the earth. Surely Allah does not like whoever is arrogant, boastful. Be moderate in your pace. And lower your voice, for the ugliest of all voices is certainly the braying of donkeys.” (31:18-19) He forbids his son from walking in a boastful manner and he advises him to be humble instead. He also tells his son to lower his voice, instead of speaking loudly.
These are pieces of advice from Luqman, which are taken directly from the Holy Qur'an and explained by mufassir Ibn Kathir. There are more advices from Luqman which are found through authentic narrations from the Messenger of Allah ﷺ, which can be found in the book Hikmat Luqman. This book compiles all of Luqman's advices, even those from the Holy Qur'an.
It was narrated by Damurah from As-Sari ibn Yahya that Luqman said to his son, “O my son! If you come to a people's setting, start them with salutation by saying Assalamu Alaykum wa Rahmatullahi wa Barakatuh, then, take a side and do not utter a word till they speak. If you find them observing the Remembrance of Allah, join them. But, if they observe anything else, turn away from them and seek others who remember Allah Almighty.” (Hikmat Luqman)
Some scholars were of the opinion that Luqman was a Prophet. However, the majority consensus is that Luqman was not a Prophet, but rather, he was one of the holy men who were close to Allah, similar to another man named Dhul-Qarnayn. Allah knows best.
Sources
Holy Qur'an - Surah Luqman
Ibn Kathir - Tafsir on Surah Luqman (ayah 12-19)
Naseem Ahmad Ghazi - Hikmat e-Luqman