The Prophet (peace be upon him and his progeny) said:
اِذا اَرادَ اللّهُ بِقَوْم خَيْراً أَهْدَى اِلَيْهِمْ هَدِيَّةً. قالُوا وَ ما تِلْكَ الْهَدِيَّة؟ قالَ: اَلضَّيْفُ
When God wills happiness and prosperity for a nation, he will bestow on them a gift. They asked: ‘what is that gift’. He replied: a ‘guest’. 1
That is true. Guest is a gift from God, a valuable and honorable gift. However, material world in which all affections are lost, has no value for a guest. It treats him as troublesome and strange and unwelcome. So it rarely happens that someone invites another or gets invited unless there is a selfish reason relating to business or wealth or politics.
In Islamic countries and families in which religious customs are still alive, a guest is honored and respected as a divine gift notwithstanding the absence of family relationship or any ulterior motives.