Asking forgiveness of sins in advance (Not saying all priests allow this, but some do)
Forgiveness of sin also ties in with the Sacrament of the Holy Eucharist.
Paul talks about having the soul cleared of sin before communion
St Paul to the Corinthians: 11: 23--30
 For I have received of the Lord that which also I delivered unto you, that the Lord Jesus, the same night in which he was betrayed, took bread.  And giving thanks, broke, and said: Take ye, and eat: this is my body, which shall be delivered for you: this do for the commemoration of me.  In like manner also the chalice, after he had supped, saying: This chalice is the new testament in my blood: this do ye, as often as you shall drink, for the commemoration of me.
 For as often as you shall eat this bread, and drink the chalice, you shall shew the death of the Lord, until he come. ...  Therefore whosoever shall eat this bread, or drink the chalice of the Lord unworthily, shall be guilty of the body and of the blood of the Lord. ...  But let a man prove himself: and so let him eat of that bread, and drink of the chalice. ...  For he that eateth and drinketh unworthily, eateth and drinketh judgment to himself, not discerning the body of the Lord. ...  Therefore are there many infirm and weak among you, and many sleep.
 "Or drink": Here erroneous translators corrupted the text, by putting "and drink" (contrary to the original) instead of "or drink".
 "Guilty of the body": not discerning the body. This demonstrates the real presence of the body and blood of Christ, even to the unworthy communicant; who otherwise could not be guilty of the body and blood of Christ, or justly condemned for not discerning the Lord's body.
 "Drink of the chalice": This is not said by way of command, but by way of allowance, viz., where and when it is agreeable to the practice and discipline of the church.
St Paul to the Corinthians: 2: 14 .3: 12-13
 But the sensual man perceiveth not these things that are of the Spirit of God; for it is foolishness to him, and he cannot understand, because it is spiritually examined.
 "The sensual man": The sensual man is either he who is taken up with sensual pleasures, with carnal and worldly affections; or he who measureth divine mysteries by natural reason, sense, and human wisdom only. Now such a man has little or no notion of the things of God. Whereas the spiritual man is he who, in the mysteries of religion, takes not human sense for his guide: but submits his judgment to the decisions of the church, which he is commanded to hear and obey. For Christ hath promised to remain to the end of the world with his church, and to direct her in all things by the Spirit of truth.
 Now if any man build upon this foundation, gold, silver, precious stones, wood, hay, stubble:  Every man's work shall be manifest; for the day of the Lord shall declare it, because it shall be revealed in fire; and the fire shall try every man's work, of what sort it is.
 "Upon this foundation": The foundation is Christ and his doctrine: or the true faith in him, working through charity. The building upon this foundation gold, silver, and precious stones, signifies the more perfect preaching and practice of the gospel; the wood, hay, and stubble, such preaching as that of the Corinthian teachers (who affected the pomp of words and human eloquence) and such practice as is mixed with much imperfection, and many lesser sins. Now the day of the Lord, and his fiery trial, (in the particular judgment immediately after death,) shall make manifest of what sort every man's work has been: of which, during this life, it is hard to make a judgment. For then the fire of God's judgment shall try every man's work. And they, whose works, like wood, hay, and stubble, cannot abide the fire, shall suffer loss; these works being found to be of no value; yet they themselves, having built upon the right foundation, (by living and dying in the true faith and in the state of grace, though with some imperfection,) shall be saved yet so as by fire; being liable to this punishment, by reason of the wood, hay, and stubble, which was mixed with their building.  Every man's work shall be manifest; for the day of the Lord shall declare it, because it shall be revealed in fire; and the fire shall try every man's work, of what sort it is.  If any man's work abide, which he hath built thereupon, he shall receive a reward.  If any man's work burn, he shall suffer loss; but he himself shall be saved, yet so as by fire.<form action="http://www.drbo.org/cgi-bin/contact" method="post" name="cf"></form>
John 6: Jesus explains Holy Eucharist.
 I am the living bread which came down from heaven.  If any man eat of this bread, he shall live for ever; and the bread that I will give, is my flesh, for the life of the world.  The Jews therefore strove among themselves, saying: How can this man give us his flesh to eat?  Then Jesus said to them: Amen, amen I say unto you: Except you eat the flesh of the Son of man, and drink his blood, you shall not have life in you.  He that eateth my flesh, and drinketh my blood, hath everlasting life: and I will raise him up in the last day.
 "Eat the flesh of the Son of man and drink his blood": To receive the body and blood of Christ, is a divine precept, insinuated in this text; which the faithful fulfil, though they receive but in one kind; because in one kind they receive both body and blood, which cannot be separated from each other. Hence, life eternal is here promised to the worthy receiving, though but in one kind. Ver. 52. If any man eat of this bread, he shall live for ever; and the bread that I will give, is my flesh for the life of the world. Ver. 58. He that eateth me, the same also shall live by me. Ver. 59. He that eateth this bread, shall live for ever.
 For my flesh is meat indeed: and my blood is drink indeed.  He that eateth my flesh, and drinketh my blood, abideth in me, and I in him.  As the living Father hath sent me, and I live by the Father; so he that eateth me, the same also shall live by me.  This is the bread that came down from heaven. Not as your fathers did eat manna, and are dead. He that eateth this bread, shall live for ever.  These things he said, teaching in the synagogue, in Capharnaum.
 Many therefore of his disciples, hearing it, said: This saying is hard, and who can hear it?  But Jesus, knowing in himself, that his disciples murmured at this, said to them: Doth this scandalize you?  If then you shall see the Son of man ascend up where he was before?  It is the spirit that quickeneth: the flesh profiteth nothing. The words that I have spoken to you, are spirit and life.  But there are some of you that believe not. For Jesus knew from the beginning, who they were that did not believe, and who he was, that would betray him.
 "If then you shall see": Christ by mentioning his ascension, by this instance of his power and divinity, would confirm the truth of what he had before asserted; and at the same time correct their gross apprehension of eating his flesh, and drinking his blood, in a vulgar and carnal manner, by letting them know he should take his whole body living with him to heaven; and consequently not suffer it to be as they supposed, divided, mangled, and consumed upon earth.
 "The flesh profiteth nothing": Dead flesh separated from the spirit, in the gross manner they supposed they were to eat his flesh, would profit nothing. Neither doth man's flesh, that is to say, man's natural and carnal apprehension, (which refuses to be subject to the spirit, and words of Christ,) profit any thing. But it would be the height of blasphemy, to say the living flesh of Christ (which we receive in the blessed sacrament, with his spirit, that is, with his soul and divinity) profiteth nothing. For if Christ's flesh had profited us nothing, he would never have taken flesh for us, nor died in the flesh for us.
 "Are spirit and life": By proposing to you a heavenly sacrament, in which you shall receive, in a wonderful manner, spirit, grace, and life, in its very fountain.
 And he said: Therefore did I say to you, that no man can come to me, unless it be given him by my Father.  After this many of his disciples went back; and walked no more with him.  Then Jesus said to the twelve: Will you also go away?  And Simon Peter answered him: Lord, to whom shall we go? thou hast the words of eternal life.  And we have believed and have known, that thou art the Christ, the Son of God.
 Jesus answered them: Have not I chosen you twelve; and one of you is a devil?  Now he meant Judas Iscariot, the son of Simon: for this same was about to betray him, whereas he was one of the twelve.