"Therefore whoever eats the bread or drinks the cup of the Lord unworthily will have to answer for the body and blood of the Lord. A person should examine himself, and so eat the bread and drink the cup. For anyone who eats and drinks without discerning the body, eats and drinks judgment* on hims...
"Therefore whoever eats the bread or drinks the cup of the Lord unworthily will have to answer for the body and blood of the Lord. A person should examine himself, and so eat the bread and drink the cup. For anyone who eats and drinks without discerning the body, eats and drinks judgment* on himself." - 1 Corinthians 11:27-29
Fr. Mike explains that receiving Holy Communion in a state of mortal sin, is itself a mortal sin. However, he also advises that if you’re genuinely uncertain about whether you’re in a state of mortal sin, you should go ahead and receive Communion. The reason is that true mortal sin requires three conditions:
Grave matter
Full knowledge
Deliberate consent
If you’re honestly unsure, the third condition isn’t fully met — meaning it can’t be a mortal sin.