In Luke 22:19 he uses the word “given” in his description of the sacrament. In Paul’s description he does not use the same word.

With regards about when it is and isn't appropriate to take the sacrament 1 Cor 11:27-29 is basically saying that a man should decide himself if he be worthy to do so, in affect allowing him to possibly take it unworthily. In 3 Nephi 18:28-29 the counsel given is that if we know that a man be unworthy and he is taking the sacrament it is our duty to inform the bishopric in an effort to protect him.

If a man takes the sacrament unworthily he is bringing damnation to his soul.

The sacrament is something that we must be preparing to partake of with an endless amount of effort. We need to remember the covenants that we made, not only on Sundays, but throughout the entire week. A way to do this is by striving to learn the importance that the sacrament plays on out lives, through scripture study, the temple, Ensign articles, and conference talks. We must be constantly striving to be worthy when the next Sunday comes around.