how grave a sin or what nature of sin would you consider one might commit that would require one to confess before approaching the chalice? What sins does communion forgive? Does it forgive all sins, and if so is there ever a reason to not approach the chalice aside from not fasting properly? I'm really not baiting... just curious.
The wording of this question, I think, is the problem with why this issue is so difficult to agree on.
There are sins for which the epitimia
("therapeutic correction") is that we abstain from Communion for a period of time even after Confessing them. I should know, because I have confessed such sins. If I have Confessed a sin and had the prayer of absolution offered in the Mysterion of Confession, how is it that I must still abstain from the Holy Gifts until my Confessor gives me permission to receive them? Is my sin not forgiven?
No. That is not what it is about.
Holy Communion is not a reward for being sinless. Holy Communion is a completely seperate Mysterion to the Mysterion of Confession.All sin
requires Repentance, whether or not one intends to receive Holy Communion next Liturgy they attend. We don't repent of sin simply so that we can Commune. The Mysterion of Confession is a healing Mysterion of the Church, whereby our repentance is witnessed by the Church in the person of the Priest. But is this the only way our sins are forgiven? Every time we make a bow in the presence of the Church, the Church is witnessing our repentance, in fact, a "bow" is called a "metanoia" ("repentance") in Koine. Every time we say the Lord's Prayer, we are asking forgiveness for our sins on the condition that we forgive those who have sinned against us. The gravity of our sin is not the question, but rather, the sincerity of our repentance. Confessing our sins before another person who acts on behalf of the Church is a sign of the sincerity of our Repentance. It is our repentance which attains our forgiveness, not some magic words pronounced over us. The "prayer of absolution" has no "magic power" to forgive sins we have not repented of.
St. Mary of Egypt Communed in the Church of St. John the Baptist on the banks of the river Jordan on the day she repented of a lifetime of fornication, harlotry and leading others to sin, and she Confessed her sin to a Priest 47 years later, and Communed again. So the question is not "how grave a sin", but rather, "how sincere the repentance". For us who are not Saints but are striving to become Saints, a good guage of our repentance of our sins is our willingness to confess them to the Church. If we hold back from Confessing a sin to our Confessor, how sincere is our repentance of it?