Why worship the guru?
We offer respect to Srila Prabhupada, our guru, because we are indebted to him for giving us knowledge of Krishna, but we don't worship him as God Himself.
Worship of Krishna's devotee is done according to Krishna's direction, and that direction is given and understood through a guru or teacher. The same principle applies in all traditions; Muhammad was a teacher of Islam, the Rabbi is the teacher for a Jewish person, the priest or even Christ himself is the teacher for the Christian, and the Pope is the teacher for the Catholic. Trying to interpret scripture based on one's speculation and limited understanding is not recommended.
We receive our understanding of how to worship the Deity of the Lord from scripture and from our spiritual master. One must not only carefully follow the procedure of worship but also cultivate the proper consciousness of the worship. The principle is to offer some service to God with love and devotion. He appears in His deity form to receive that worship for our benefit, because without serving Him we will serve so many other lesser things and persons like movie stars, sports heroes, politicians, etc.
Krishna already has everything, but still we try to offer something, with love. When we do, He promises to accept it; just like a parent who accepts some insignificant gift from a loving child. If we follow the rules of worship under proper guidance, and we have the proper consciousness, then the Lord by His mercy receives our worship. And Krishna Himself says that one who claims to be His devotee is not His devotee, but one who is a devotee of His devotee is actually His devotee.