In Christ's high priestly prayer found in John 17, Christ acts as high priest for the elect people of God, praying for His covenant people, whom the Father has given Him:
I have manifested your name to the people whom you gave me out of the world. Yours they were, and you gave them to me, and they have kept your word. (John 17:6-7, ESV)These are the ones for whom Christ prays as priest in this chapter - they are secure in Him, and cannot be taken from His hand.
While I was with them, I kept them in your name, which you have given me. I have guarded them, and not one of them has been lost except the son of destruction, that the Scripture might be fulfilled. (John 17:12, ESV)Those who are Christ's are His securely - for the Father has so secured them that they cannot be removed, by any trial, or any temptation. These know the Lord's voice, as sheep know the voice of their shepherd, and they follow Him. This following is no mere "going in the general direction" but a walking in His steps.
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. (John 10:27-31, ESV)
Later in Christ's high priestly prayer, he speaks of those who come after His death, who are equally secure in Him -
I do not ask for these only, but also for those who will believe in me through their word, that they may all be one, just as you, Father, are in me, and I in you, that they also may be in us, so that the world may believe that you have sent me. The glory that you have given me I have given to them, that they may be one even as we are one, I in them and you in me, that they may become perfectly one, so that the world may know that you sent me and loved them even as you loved me. (John 17:20-23, ESV)These who Christ prays for are said to believe in Him, and to "all be one", and as the Father is in Christ, and Christ in the Father, they are said to be in them, for the purpose of showing the World who God is and that Christ the Lord has been sent by the Father. They are said to be "perfectly one".
Now fast forward to John's epistle that will form the basis for our family worship for the coming weeks. In chapter 2, the Apostle writes of those who know the Father - those whom Christ prays for above, and speaks of as being securely His, "one with Him" and with the Father, and also as being "in Him":
Whoever says “I know him” but does not keep his commandments is a liar, and the truth is not in him, but whoever keeps his word, in him truly the love of God is perfected. By this we may know that we are in him: whoever says he abides in him ought to walk in the same way in which he walked. (1 John 2:4-6)These also, these who know God and have the truth and love of God perfected in them, walk according to His ways - not a perfect resemblance, of course, as John goes on to say - but those who are Christs; the elect of God, those who may be said to be "in Christ" are those who live lives of humble obedience and entrust all to Him. These are by no means sinless individuals, but those who recognize their sin, lament and forsake it, and know, according to John's word, that
If we say we have no sin, we deceive ourselves, and the truth is not in us. If we confess our sins, he is faithful and just to forgive us our sins and to cleanse us from all unrighteousness. If we say we have not sinned, we make him a liar, and his word is not in us. (1 John 1:8-10, ESV)That is, the elect know who they are, and know also who they are in Christ: forgiven sinners, washed in His blood, cleansed from unrighteousness by His work. They walk lives characterized by grateful obedience and gracious remembrance of what they have received from God. Importantly it is these that the Apostle characterizes as being "in Christ" - and he distinguishes those who are in Him from those who are not.
Everyone who makes a practice of sinning also practices lawlessness; sin is lawlessness. You know that he appeared to take away sins, and in him there is no sin. No one who abides in him keeps on sinning; no one who keeps on sinning has either seen him or known him. (1 John 3:4-6, ESV)Now, finally - now that we have seen where John's going with this argument - that those who abide in Christ, those who are in Him, secure by the Father's bidding to be His eternally, walk humbly before their God, what of these others who do not, or who "fall away"? John's answer comes starkly in chapter 2:
They went out from us, but they were not of us; for if they had been of us, they would have continued with us. But they went out, that it might become plain that they all are not of us. (1 John 2:19, ESV)They "fell away" not because God's promises failed, not because they were "in" and then became "out" by some failure of His grasp upon them, but because they were never "in Christ". Brothers and sisters, identity as one of God's children is a secure identity - an eternal promise that bears up in fruition of sanctification throughout one's life. Those who are in Christ are eternally so - never, as Christ said, recorded in John's Gospel, can the devil snatch any of those precious lambs from their Shepherd's arms.
If there are those who are in the church, and who sit side by side with us, who up and leave and deny Christ, they are lost not because they were "in" and now are "out". They are lost because they were never in the bond of peace with the Lord. His bonds are held fast by His unassailable strength. As temptation arises, recall this to mind, for it is the ground of Hope - the Lord's promises are secure; resting in them, forsaking the world, and clinging to Christ for ALL of your righteousness, we may know that we are in Him and He in us... we will not walk perfectly, we will not be perfectly free of sin, not on this side of glory. But if our trust is in Him, he will clean us, and walk with us, and preserve us. Be not afraid - but rest in Christ. He has done all to secure those who are in Him.