The reason is that the guests bring with them the blessings. They bring with them happiness and some bonding which makes you feel owned, liked and worthy.
They make you feel that they trust you. Guests are people who come to make you realize that for them you are important. They care to meet you and spend time with you.
Think about it..how their arrival makes everyone smile..giving gestures of welcome and thankfulness.
Whether they stay with you for a while or some more still your home is completely changed beaming with pleasant vibes and you can notice how you suddenly feel active and vibrant to make them comfortable and offer them your best in everything.
Not to mention the best food that you try to offer them, the best cutlery you use and and and...the best way you present yourself in terms of clothes and manners!!
So to be more specific...guests come to make you lively and energetic with all the positive energy. They are a blessing indeed, sent by God to make you feel loved and appreciated, to make you feel trusted and to bring out the best in you.