[Natural Law]

"What about the necessity aspect?"

It is in the liturgy, especially in the divine sacrifice of the Eucharist, that "the work of our redemption is accomplished," and it is through the liturgy especially that the faithful are enabled to express in their lives and manifest to others the mystery of Christ and the real nature of the true Church.

The Church is a "communion of saints": this expression refers first to the "holy things" (sancta), above all the Eucharist, by which "the unity of believers, who form one body in Christ, is both represented and brought about"

[armydoc]

It is in the liturgy, especially in the divine sacrifice of the Eucharist, that "the work of our redemption is accomplished," and it is through the liturgy especially that the faithful are enabled to express in their lives and manifest to others the mystery of Christ and the real nature of the true Church. The Church is a "communion of saints": this expression refers first to the "holy things" (sancta), above all the Eucharist, by which "the unity of believers, who form one body in Christ, is both represented and brought about"

I can't tell by this answer whether or not you believe that taking the Eucharist is necessary for salvation. Could you clarify?