Is it obligatory to continue calling a person who persists in sin?

Question:
The questioner says: I am a young military man in Dammam, and I find among the youth at work—most of them are from the Awthas tribe, who are the vast majority—many instances of what is wrong, such as abandoning the prayer in congregation and smoking. I have started speaking to them about it, as well as to those I live with in the housing, although there are some righteous young men, but they are few. I restrain myself in the path of calling them, hoping that Allah will guide them. My father and brothers live in Riyadh. The question is: Am I required to continue with what I am doing, or not? Also, I want to perform jihad and I want to get married; which should I prioritize? May Allah reward you with good.

Answer:
As for being patient in calling these people and advising them, along with our good brothers, this is a good matter. Do not be distressed, do not despair, and do not give up. Rather, be patient and meet them with the call to Allah and advice to them, until they straighten out in the prayer in congregation, until they leave off smoking, and until they abandon the evil. You must be serious and enjoin what is right and forbid what is wrong with your good brothers. Cooperate in righteousness and piety, and know that 'Umar ibn al-Khattab (may Allah be pleased with him) said: "Whoever guides to good, he has a share of the reward of the one who does it." And it was said: "If Allah guides one person through you, that is better for you than the world and all that is in it." When a person calls, and Allah guides a person through his hands, it is a great reward for him. So you should not despair or be overwhelmed. If you wish, regarding the matter of jihad, jihad takes precedence over marriage. If you get married, there is no harm, but with consideration for your parents. If your parents are at war, then do not get married until you have their permission.