The New Covenant is all about Communion with God. For God to dwell in and nourish us is the right and just order of things for man. This is the relationship that Adam shattered and forfeited in Eden at the Fall, bent on being autonomous as he was. We need this indwelling constantly, and need to nurture this relationship ourselves. But in Catholic theology, communion with God is broken with grave-or mortal-sin, sins against love where love, itself, is destroyed in us. We can lose our salvation IOW. In this case we’re to refrain from the Eucharist, echoing and acknowledging by our actions what has already transpired within, a broken relationship with our Creator. With a true change of heart we can still repent, however, and confess our sins so we may be healed with the Sacrament of Reconciliation, whereupon our relationship is healed, our sins forgiven and communion restored. In like fashion we now resume partaking of the Eucharist.
In this way the sacraments give us a means to live or act out our faith in the most basic ways. It can all be done mechanically and insincerely, of course, in which case the sacraments may not be efficacious, but that’s only human, something to be on guard against, something to outgrow.
The point of the Eucharist: “Apart from Me you can do nothing” John 15:5, but, “With God all things are possible” Matt 19:26. The reason the Eucharist is the center of the Mass is because communion with God is eternal life.