115 Now it cannot be over-emphasized that the eucharistic sacrifice of its very nature is the unbloody immolation of the divine Victim, which is made manifest in a mystical manner by the separation of the sacred species and by their oblation to the eternal Father. Holy communion pertains to the integrity of the Mass and to the partaking of the august sacrament; but while it is obligatory for the priest who says the Mass, it is only something earnestly recommended to the faithful.
Source: Mediator Dei (Vatican.va)