Because it is believed that the spirit of the dead becomes a Buddha upon completion of the funeral, the address "Goreizen" (to the spirit) is used before completion of the funeral and the address "Gobutsuzen" (to the Buddha) is used after the funeral.
葬儀が終わって故人の霊魂が成仏した後は「御仏前」、それまでは「御霊前」との考え方。