The Book of Mormon: Chapter Fourty-Two: 3 Nephi 18:22–32
22And behold, ye shall meet together oft; and ye shall not forbid any man from coming unto you when ye shall meet together, but suffer them that they may come unto you and forbid them not;
23But ye shall pray for them, and shall not cast them out; and if it so be that they come unto you oft ye shall pray for them unto the Father, in my name.
24Therefore, hold up your light that it may shine unto the world. Behold I am the light which ye shall hold up—that which ye have seen me do. Behold ye see that I have prayed unto the Father, and ye all have witnessed.
Jesus Christ instituted in ancient America, the same ordinance of the Sacrament, that He instituted in the upper room, prior to His death. What an amazing blessing to be able to partake of bread and water weekly, gaining forgiveness of our sins as we repent and self-examine during Sacrament meeting. Perfection is not required for taking the Sacrament, but striving to be ever worthy is, as indicated in these words:
Emphasizing as I have, the importance of worthiness in partaking of the sacrament of our Lord, maybe there are some of you, I hope not, that have a feeling you have been unworthily partaking. Remember, we have in the Church the principles of repentance, and of forgiveness. Certainly one who truly repents with all their heart and [does] the works of righteousness can be forgiven and the Lord will remember their sins no more. Such an individual can reinstate himself [with the help and counsel of priesthood leaders] to worthily partake of the emblems of our Lord (Delbert L. Stapley, The Sacrament, Brigham Young University Speeches of the Year [Provo, 8 May 1956], p. 9).
To view an overview of what to expect in an LDS “Mormon” Sacrament Meeting, check out this video.