1 Cor 11:30 is talking about coming together for Communion - the Lord's Supper. It says many are weak and sick because they eat and drink communion unworthily - bringing
damnation upon themselves.
What is communion? What is the Lord's Supper? It was Jesus, the night of his betrayal (the beginning of his 3 days "in the earth") partaking of the Passover feast.
Luke 22:7 Then came the day of unleavened bread, when the passover must be killed.
8 And he sent Peter and John, saying, Go and prepare us the passover, that we may eat.
Of course, the Passover feast is prophecy of Jesus Christ. The lamb who is slain, and the blood that causes the destroyer to pass over. If you look at the passover feast from Exodus, it says that they are not to eat leavened bread, and leaven isn't to even be found in their house during the feast.
Exd 12:19 Seven days shall there be no leaven found in your houses: for whosoever eateth that which is leavened, even that soul shall be cut off from the congregation of Israel, whether he be a stranger, or born in the land.
Jesus talks about leaven:
Matt 16:1 The Pharisees also with the Sadducees came, and tempting desired him that he would shew them a sign from heaven.
Matt 16:4 A wicked and adulterous generation seeketh after a sign; and there shall no sign be given unto it, but the sign of the prophet Jonas. And he left them, and departed.
Matt 16:6 Then Jesus said unto them, Take heed and beware of the leaven of the Pharisees and of the Sadducees.
Matt 16:12 Then understood they how that he bade [them] not beware of the leaven of bread, but of the doctrine of the Pharisees and of the Sadducees.
Remember 1 Cor 11:19 - which is context for verse 30:
1 Cor 11:19 For there must be also heresies among you, that they which are approved may be made manifest among you.
The Apostle Paul brings this up in Galatians as well - in a virtual echo of 1 Cor 11.
Gal 5:4 Christ is become of no effect unto you, whosoever of you are justified by the law; ye are fallen from grace.
5 For we through the Spirit wait for the hope of righteousness by faith.
6 For in Jesus Christ neither circumcision availeth any thing, nor uncircumcision; but faith which worketh by love.
He prefaces by saying that salvation is by faith, not by the law. He talks about those who were trying to say that the Gentiles needed to be circumcised to be saved (in other words, follow The Law to attain salvation).
Gal 5:7 Ye did run well; who did hinder you that ye should not obey the truth?
8 This persuasion [cometh] not of him that calleth you.
9 A little leaven leaveneth the whole lump.
He says they were believing right, until someone introduced this false doctrine (persuasion not of Him that calleth them). He then calls the heresy (salvation by works) "
leaven".
Gal 5:10 I have confidence in you through the Lord, that ye will be none otherwise minded: but he that troubleth you shall bear his judgment, whosoever he be.
Paul then says that the person with the heretical doctrine will "bear his judgment". The Hebrew word for Judgment here is
krima. This is the same word (krima) that is translated "damnation" in 1 Cor 11:29
1Cor 11:29 For he that eateth and drinketh unworthily, eateth and drinketh damnation to himself, not discerning the Lord's body.
Paul goes on to say in Gal5:12 that he would that the persons who trouble the saints with heresy would be cut off - again a reference to Passover and Exodus 12:19.
Gal 5:12 I would they were even cut off which trouble you.
Paul brings it all together in Galatians 5 by saying why and what they should do:
Gal 5:13 For, brethren, ye have been called unto liberty; only [use] not liberty for an occasion to the flesh, but by love serve one another.
14 For all the law is fulfilled in one word, [even] in this; Thou shalt love thy neighbour as thyself.
And finally, I would remind everyone of what is said in Psalms regarding the day after passover when the Israelites left Egypt:
Psalms 105:37 He brought them forth also with silver and gold: and [there was] not one feeble [person] among their tribes.
So when it speaks of taking communion unworthily, it is referring to the non-believer - one without faith in Jesus Christ - because the only way you can be unworthy is to be unsaved (not made righteous by the blood of Jesus), and the only way to be saved is by faith, not by works. Communion represents the direct communion with God (the Holy of Holies veil being torn), therefore those not redeemed by the blood of Jesus are judged - that is how sickness comes upon them. The sin within them is judged in the presence of God.
Of course, you are not covered by righteousness if you are in unforgiveness (Mar 11:26), this this would make one "unworthy" as well.