How do we deal with Islamic groups?

In the name of Allah, the Most Gracious, the Most Merciful.
Praise be to Allah, and may peace and blessings be upon the Messenger of Allah. As for what follows, this is one of the tapes from the Al-Huda wa al-Nur series of scholarly lessons and legal rulings by our Shaykh, Muhammad Nasir al-Din al-Albani (may Allah preserve him). We ask Allah to benefit everyone with it. And now, with tape number one hundred and seventy-one.

The Shaykh: And these people, who do not care about correcting the creed and correcting concepts, are opposed by others who are the exact opposite of them. These others care, as is obligatory, about knowing the truth in matters where people differ. However, they oppose that first group with the strongest opposition. The truth lies between these two groups. Therefore, our position toward Islamic groups must be one of believing brotherhood. If a Muslim sees an error in his brother, or even if he sees a sin, it is not permissible for him to oppose him. Rather, he must advise him, and his advice should be with the gentleness and wisdom commanded in the Book and the Sunnah. It should be noted by those who care about knowing the truth in matters where people differ that if people are in error, they are like patients who must be treated with complete sincerity and complete gentleness. It is not permissible to treat them with harshness and severity. And so, Allah (Mighty and Majestic) addressed His Prophet (peace be upon him) to teach us: Therefore, our call, which is confined to following the Book and the Sunnah upon the methodology of the righteous predecessors, does not oppose any of the Islamic groups for the sake of their persons. Rather, it disagrees with them in some of their ideas or methodologies. This obligates us to advise them and call them to the truth, no matter how far they stray or how far they depart from our path, which is the path of our Lord.