"And fulfil the covenant of Allah when you have made a covenant, and do not break the oaths after making them fast, and you have indeed made Allah a surety for you; surely Allah knows what you do (16:91)."
 

The purpose of this verse is to indicate that any Muslim who makes a promise to Allah or to people must keep it and must not breach it.

"Call to the way of your Lord with wisdom and goodly exhortation, and have debates with them in the best manner; surely your Lord best knows those who go astray from Hi. path, and He knows best those who follow the right way (16:125)."

This refers to the fact that to promote religion, a Muslim must converse with people according to their understanding and in a way that is beneficial to them. However, if he fails to guide a person through logic and advice then he must debate in the best manner, which is one of the means of proving something, to guide him towards truth.

"And when the Qur'an is recited, then listen to it and remain silent, that mercy may be shown to you (7:204)."

"0 you who believe! Obey Allah and obey the Prophet and those in authority from among you; then if you quarrel about anything, refer it to Allah and the Prophet, if you believe in Allah and the Last Day; this is better and very good in the end (4:59)."