This is the law of agency. A person who is sent represents the person who sent him. An apostle is a person who is sent out. We understand this word in a religious sense. However, this is a commonly understood principle in law. If I sent someone to do business for me, they would have all the authority that I have to conduct the business for which I sent them. A person who receives them receives me.
In this verse, we understand that God sent Jesus. Anyone who receives Jesus, receives God. If Jesus sends us, we have all the authority of Jesus to conduct the business for which He sent us. This authority is all the authority of God Himself.
God >>>> Jesus >>>> apostles (us)