Sometimes I envy the Catechism, it says this all so well:
s. 1136 Liturgy is an action of the whole Christ (Christus totus). Those who now celebrate it without signs are already in the heavenly liturgy, where celebration is wholly communion and feast.
1137 The book of Revelation of St John read in the Church’s liturgy, first reveals to us ‘A throne stood in heaven, with one seated on the throne’: ‘the Lord God’. it then shows the Lamb, ‘standing as though it had been slain’: Christ crucified and risen, the one high priest of the sanctuary, the same one ‘who offers and is offered, who gives and is given’.
1138 ‘Recapitulated in Christ’ these are the ones who take part in the service of the praise of God and the fulfilment of his plan: the heavenly powers, all creation (the four living beings), the servants of the Old and New Covenant (the twenty-four elders), the new People of God (the one hundred and forty-four thousand), especially the martyrs ‘slain for the word of God’, and the all holy Mother of God (the Woman), the Bride of the Lamb, and finally ‘a great multitude which no one could number, from every nation, from all tribes and peoples and tongues’.
1139 It is in this eternal liturgy that the Spirit and the Church enable us to participate whenever we celebrate the mystery of salvation in the sacraments.
1141 This ‘common priesthood’ is that of Christ the sole priest, in which all his members participate.
1142 The ordained minister is at it were an ‘icon’ of Christ the priest.
By the way, I found it posted here