Doesn't the word depart have a meaning to you? It means to leave. You cannot leave from a place you are not at.
Also, one can be put out of the Church according to St. PAUL. Christ is not coming back to collect me or you but for His Church. Our job is to be a part of that Church.
They personally depart the faith, but they do not depart their faith as they did not have faith that came from God who preserves His saints.
Who does the preserving? Us or God?
We 'are kept by the power of God through faith for salvation'.
The means God uses here by His power is faith.
God's power grants to us our faith. All things work to the good of them that love God who are the called according to His purpose. ALL things! So its impossible for anything to happen that would cause His people to abandon their faith as that would be a bad thing.
1 Peter 1
3 Blessed be the God and Father of our Lord Jesus Christ, who according to His abundant mercy has begotten us again to a living hope through the resurrection of Jesus Christ from the dead, 4 to an inheritance incorruptible and undefiled and that does not fade away, reserved in heaven for you, 5 who are kept by the power of God through faith for salvation ready to be revealed in the last time.
6 In this you greatly rejoice, though now for a little while, if need be, you have been grieved by various trials, 7 that the genuineness of your faith, being much more precious than gold that perishes, though it is tested by fire, may be found to praise, honor, and glory at the revelation of Jesus Christ, 8 whom having not seen you love. Though now you do not see Him, yet believing, you rejoice with joy inexpressible and full of glory, 9 receiving the end of your faith—the salvation of your souls.
God preserves those He calls to be saved.
Jude New King James Version (NKJV)
Greeting to the Called
1 Jude, a bondservant of Jesus Christ, and brother of James,
To those who are called, [a]sanctified by God the Father, and preserved in Jesus Christ:
2 Mercy, peace, and love be multiplied to you.
All the problems with understanding this goes away if you stop believing God calls all men to be saved! That call is a sovereign decree, those not called to be saved wont be. Believers are born again before they have their faith.
John 3, that word see means to perceive. Unless first born again, a person will not want anything to do with Christ as the Lord God come in the flesh as their savior. All of it will just be foolishness to them.
3 Jesus answered and said to him, “Most assuredly, I say to you,
unless one is born again, he cannot see the kingdom of God.”
4 Nicodemus said to Him, “How can a man be born when he is old? Can he enter a second time into his mother’s womb and be born?”
5 Jesus answered, “Most assuredly, I say to you, unless one is born of water and the Spirit, he cannot enter the kingdom of God. 6 That which is born of the flesh is flesh, and that which is born of the Spirit is spirit. 7 Do not marvel that I said to you, ‘You must be born again.’ 8 The wind blows where it wishes, and you hear the sound of it, but cannot tell where it comes from and where it goes. So is everyone who is born of the Spirit.”
We are born again by His will, not our will, you can not control where the wind will blow.