Because he is a triune being consisting of three parts. God is the soul of the Godhead. Jesus is the body of the Godhead. The Holy Spirit is the spirit of the Godhead. God made man in His image.
Man consists of body, soul, and spirit.
The mortal man's body decays and rots until death when the spirit and soul depart. After Jesus rose from the grave, he had to leave earth so he could send the Holy Spirit. It meant that he was unable to send the Spirit until he was reunited with His soul, God. Body, soul, and spirit are connected in ways that we don't yet understand. God is an infinite being.