Technically, it is the work of the Church, which equals all the people gathered together. I only harp on this because some people use the phrase to mean that traditions are not useful and can be discarded casually by the liturgy committee. Interestingly, the Orthodox Church takes this phrase rather literally: the liturgy is the common action of the Church, so priests do not celebrate the liturgy alone as they do in the RC Church--nor do they celebrate multiple liturgies. It is the gathering of all at one time on the "eighth day" in order to experience the divine kingdom.