Lord’s Evening Meal?
In short, this is because Jehovah’s Witnesses, in contrast to the churches of Christendom, accept the Bible’s teaching that a small number of humans will gain heavenly life and the rest of God’s faithful servants will be rewarded with everlasting life on earth.
(Also see: What Do Jehovah's Witnesses Believe Regarding Physical And Heavenly Afterlives? The 144,000?; Search For Bible Truths)
When Christ instituted the New Covenant, the "communion meal" or drinking of wine and eating bread was part of enacting a formal covenant (Lk. 22:20; Mt 26:26-29; Mr 14:22-25; 1Cor.11:23-29). Those partaking were participants in the New Covenant and were to become kings and priests with him (Lk. 22:28-30).
Those to whom "God gives the Kingdom" would be a relatively small number–a "little flock,""firstfruits" (Lk.12:32; Dan 7:18,22,27). The "blood of the covenant" "inaugurated the way of entry into heaven" for these chosen ones (Heb 9:24; 10:15-20; Jer.31:31-34). The Bible states that there were to be 144,000 taken to heaven to rule as kings and priests (Rev.14:1-4; 5:9,10; 20:4-6; Heb 12:22-24). Only these 144,000 are "bought from the earth" and "have been enrolled in the heavens."
All this demonstrates that the New Covenant was the legal arrangement by which faithful humans would enter heaven as kings and priests. So ONLY participants of that covenant would partake of the emblems of Christ's blood and flesh at the celebration of the Last Supper.
There was no need for those with the earthly hope to partake of the covenant meal since they are not participants in the New Covenant. In fact, doing so would be presumptuous. Jehovah would be displeased if a person represented himself as one called to be a heavenly king and priest when he had no such calling. God executed Korah for presumptuously seeking the priesthood (Ex.28:1; Num.16:4-11, 31-35).
The new covenant will eventually bring blessings to all obedient mankind. Even though those with a(n) earthly hope do not partake of the Memorial emblems they also gain salvation by Christ's ransom.
The apostle John said: "I am writing you these things that you may not commit a sin. And yet, if anyone does commit a sin, we have a helper with the Father, Jesus Christ, a righteous one. And he is a propitiatory sacrifice for our sins, yet not for ours only but also for the whole world's" (1Jn 2:1,2). So Jesus died not only for those anointed Christians who will rule in heaven, but also for the sins of the whole world, making eternal life possible for obedient mankind in the Paradise earth now so near at hand!
So a person is not required to partake of the Memorial emblems in order to be saved by Jesus' ransom sacrifice and receive eternal life on earth. For instance, the Bible gives no indication that God-fearing people like Abraham, Sarah, Isaac, Rebekah, Boaz, Ruth, and David will ever partake of these emblems. But because of Christ's ransom they will be resurrected and we will live with them on earth!
Those of the "other sheep" or innumerable "great crowd" are not disappointed that they are not going to heaven. In fact, their desire is to enjoy the amazing blessings God gives them on earth. They are also highly favored by God; Jehovah called them "blessed" and "my people" (Isa.65:21-23; Ps.37:11; Mt.5:5).
As Jehovah's "blessed people" we look forward to fulfilling God's original purpose for humans by living forever on a paradise earth without death or sickness.
It is very obvious that Christendom's doctrine of only two ultimate destinies is incorrect. While the wicked will be destroyed, the Bible is very clear that there are actually two destinies for righteous humans. Only a small group are part of the New Covenant to be kings in heaven and the other is a great multitude of subjects who "inherit the earth."
A serious handicap for many is that they have been taught that the only future hope for righteous humans is heaven. However, this teaching ignores the fact that the Bible shows that the majority of righteous humans will inherit eternal life on earth (Rev.21:1,3,4; 2Pet.3:12-13; Ps 37:10,11,29; 104:5; Ec. 1:4).
On the other hand, the Bible teaches that only a comparatively few will be "bought from the earth" to rule as kings and priests in heaven (Rev. 14:1,3,4; Lk. 12:32; Joh 14:2-3; Heb.12:22,23). In the scriptures these 144,000 are variously described as Christ's "brothers," his "joint heirs" "sons of God" and "partakers of the heavenly calling," and etc. (Heb 2:10-12; 3:1-6; Rm. 8:14-17,29, 30; 1Pt. 1:4; 1Jn. 3:2). The 144,000 making up this "little flock" are the only humans ever seen in heaven.
Because of their belief that all good people go to heaven most religions are the ones who ignore the fact that two groups are consistently differentiated in the Bible, both who believe in Christ and gain salvation. Failure to accept this scriptural truth results in an inability to properly understand the New Covenant arrangement.
(Source: This is the chosen best answer given by Bar_Anerges to this question.)
(For more, see the 144,000 Category.)
How Does One Know if They Are of the Anointed Or Called to Heavenly Life?
Romans 8:13-17...shows that God's holy spirit, or active force, creates within anointed ones the assurance that they are destined for heavenly life. They have an unmistakable knowledge that they have been "adopted" as heavenly Sons. They are "God's children" in a special sense because of this new and special "adoption" to a heavenly life (1 Pet. 1:3-4, 23; Heb. 12:23). These are "born again" because they have this heavenly life in view rather than God's original earthly purpose for humankind. This was a new arrangement for humans put in effect only after Christ came to earth. That is why they are a "new creation." They are chosen by God directly, not because that is what they have been taught by others (Jn. 1:9-13; Jas. 1:17-18; 2 Cor. 5:17).
[It has been observed by some] that their whole outlook on life changes to embrace heavenly life. They are willing to sacrifice all earthly things, including human life. Human's natural desire is to eternally live and enjoy the beautiful things on earth. We desire beautiful sunsets, valleys and mountains. We look forward to enjoying earth's animals and having children and grandchildren. We would be happy to just continue living without ever dying. Humans naturally fight death and struggle to hold on to this life. But, those adopted as heavenly heirs no longer desire such things on a future paradise earth. Their intense and innate longing is for heavenly life (2 Cor. 5:1-5; Php. 1:21-23).
This is different than what we find in most people who have been taught by their religions that they are going to heaven. These people say they are going to heaven, but when they describe what they think it is going to be like they describe it using earthly concepts and desires. They usually just transfer earthly things and desires into heaven. Those who have the real hope of life in heaven know that they will not have earthly possessions, desires, nor fleshly bodies in heaven. So they do not make the mistake of transferring earthly life into heaven.
And if you are unsure or have to ask someone else if you are of the anointed--then you are not!
(Source: This is the answer given by Bar_Anerges to this question.)