FK, we can never be worthy except through Christ to receive the Eucharist. And we should never, ever, be so prideful as to believe that we are "worthy" to approach the sacred Mysteries. We never judge ourselves "presumptively saved". Here is what we Orthodox pray immediately before receiving communion:
"I believe and confess, Lord, that You are truly the Christ, the Son of the living God, who came into the world to save sinners, of whom I am the first. I also believe that this is truly Your pure Body and that this is truly Your precious Blood. Therefore, I pray to You, have mercy upon me, and forgive my transgressions, voluntary and involuntary, in word and deed, known and unknown. And make me worthy without condemnation to partake of Your pure Mysteries for the forgiveness of sins and for eternal life. Amen
How shall I, who am unworthy, enter into the splendor of Your saints? If I dare to enter into the bridal chamber, my clothing will accuse me, since it is not a wedding garment; and being bound up, I shall be cast out by the angels. In Your love, Lord, cleanse my soul and save me.
Loving Master, Lord Jesus Christ, my God, let not these holy Gifts be to my condemnation because of my unworthiness, but for the cleansing and sanctification of soul and body and the pledge of the future life and kingdom. It is good for me to cling to God and to place in Him the hope of my salvation. Receive me today, Son of God, as a partaker of Your mystical Supper. I will not reveal Your mystery to Your adversaries. Nor will I give You a kiss as did Judas. But as the thief I confess to You: Lord, remember me in Your Kingdom."
The Greek word "parrésia" means *boldness* or *confidence*.
We are to come BOLDLY to the throne of Grace. Not cowering in fear.
Romans 8:15 For ye have not received the spirit of bondage again to fear; but ye have received the Spirit of adoption, whereby we cry, Abba, Father.
I would agree that any worthiness would have to be by and through Christ. According to the Bible it is either proper or improper for us to partake, and Paul tells us to determine this we should do an honest assessment of ourselves (has Christ so worked in us). The Bible gives us ample evidence of what a true Christian "looks like" so we have a perfect template for us to use. Of course if we "pass" and figure it is proper for us to partake the credit and glory for this go directly to God, not to ourselves for anything we have done to make ourselves worthy.
So, when I consider myself presumptively saved it is only a reflection of whether I believe God's Biblical promises, as best as I can understand them, to be true or not. The Bible plainly shows us what a true Christian looks like so if an honest assessment leads me to think I look like that then I say I am presumptively saved, not because of me but because God's word is true. And as Metmom just showed with her verses, the Bible also says that we may know and have confidence about this. Thus, the backing for these presumptions is never ourselves, but our understanding of what God's word says and that it is true.
Here is what we Orthodox pray immediately before receiving communion:
Theological differences aside, it's a beautiful prayer.