When you wish good for others, good things come back to you. This is the law of nature.
Human is a component of nature and strongly influenced by the laws of nature. One of those rules is that you will get what you give.
When you desire good things for others, the kindness and clarity of your thoughts radiate positive and pure energy. It is this energy that will attract similar sources of energy to you.
That’s why good things will come to you. You treat everyone well, someone will be nice to you. You love people, there will be people who love you.
What you have received is even more than what you have given. That is the consant law of the nature.