What is love for the sake of Allah, and is it restricted to religious matters, excluding ordinary worldly affairs such as comradeship and neighborliness?

Love for the sake of Allah is a person's love for another's uprightness in obeying Allah's commands and abstaining from His prohibitions, not for any other worldly purpose. It is among the firmest bonds of faith and has great benefits. Among them is that it is a sign of a sound heart and strong faith, and that it is a reason for its possessor to be among the seven whom Allah will shade in His shade on a day when there is no shade but His. One must choose a friend based on piety and uprightness, for the Prophet, peace and blessings be upon him, said: "A person is on the religion of his intimate friend, so let one of you look at whom he befriends."