Some points to ponder. Jesus said that no one would be able to take His “sheep” from Him.
John 10: 27 My sheep hear My voice, and I know them, and they follow Me; 28 and I give eternal life to them, and they will never perish; and no one will snatch them out of My hand. 29 My Father, who has given them to Me, is greater than all; and no one is able to snatch them out of the Father's hand.…
Now, if a person proclaims Jesus as their Savior, which scripture also teaches cannot be done without the Father drawing them, and they are “given eternal life” who is it that will be able to “snatch them out of the Father’s hand”? I would take “no one” to include the person saved since we know that it’s Satan who would draw someone away from Christ. If they can be “snatched away” than the Father is not “greater than all”.
I don't know how much clearer it can be.
John 5:24 Truly, truly, I say to you, whoever hears my word and believes him who sent me has eternal life. He does not come into judgment, but has passed from death to life.
John 10:25-30 Jesus answered them, “I told you, and you do not believe. The works that I do in my Father's name bear witness about me, but you do not believe because you are not among my sheep. My sheep hear my voice, and I know them, and they follow me. I give them eternal life, and they will never perish, and no one will snatch them out of my hand. My Father, who has given them to me, is greater than all, and no one is able to snatch them out of the Father's hand. I and the Father are one.”
2 Corinthians 1:21-22 And it is God who establishes us with you in Christ, and has anointed us, and who has also put his seal on us and given us his Spirit in our hearts as a guarantee.
2 Corinthians 5:4-8 For while we are still in this tent, we groan, being burdened—not that we would be unclothed, but that we would be further clothed, so that what is mortal may be swallowed up by life. He who has prepared us for this very thing is God, who has given us the Spirit as a guarantee.
So we are always of good courage. We know that while we are at home in the body we are away from the Lord, for we walk by faith, not by sight. Yes, we are of good courage, and we would rather be away from the body and at home with the Lord.
Ephesians 1:13-14 In him you also, when you heard the word of truth, the gospel of your salvation, and believed in him, were sealed with the promised Holy Spirit, who is the guarantee of our inheritance until we acquire possession of it, to the praise of his glory.
Ephesians 4:30 And do not grieve the Holy Spirit of God, by whom you were sealed for the day of redemption.
Colossians 1:13-14 He has delivered us from the domain of darkness and transferred us to the kingdom of his beloved Son, in whom we have redemption, the forgiveness of sins.
Colossians 3:3 For you have died, and your life is hidden with Christ in God.
1 Peter 1:3-5 Blessed be the God and Father of our Lord Jesus Christ! According to his great mercy, he has caused us to be born again to a living hope through the resurrection of Jesus Christ from the dead, to an inheritance that is imperishable, undefiled, and unfading, kept in heaven for you, who by God's power are being guarded through faith for a salvation ready to be revealed in the last time.
http://www.freerepublic.com/focus/religion/3156607/posts?page=313#313
2 Corinthians 1:21-22 Now he which stablisheth us with you in Christ, and hath anointed us, is God; Who hath also sealed us, and given the earnest of the Spirit in our hearts.
For which the Greek, from the Byzantine, is:
2Corinthians 1:21-22 ο δε βεβαιων ημας συν υμιν εις χριστον και χρισας ημας θεος ο και σφραγισαμενος ημας και δους τον αρραβωνα του πνευματος εν ταις καρδιαις ημων
The first word in bold above is “bebaion,” the idea of confirmation, frequently used in commercial settings to confirm a bargain. Which of course makes sense of the remaining terms used here, which are also elements of a secured contract.
The second word in bold above is “sphragisamenos,” being sealed is to be marked by the signature, signet ring, or other unique proof of identity, that we belong to God, and this sealing is done by God, who is the one taking action in this verse. We do not and cannot seal ourselves. We do not, by our own powers, have access to God’s “signet ring.”
The third bolded word above is “arrabona,” and indicates what we might loosely refer to as earnest money, but in Hebrew culture conveys more the idea of a pledge of covenant, a security given as a guarantee that the deal will go through, though we only receive part payment at the beginning. See ערב for the related Hebrew stem indicating “pledge.”
Also, the man who was sinning in the Corinthian church was still considered a believer. And Paul said that the reason why some were weak and sick and some had died was because they were not taking communion in a worthy manner, sin in their lives, I'd figure.