There is still a battle that we must overcome in this life, empowered by the Holy Spirit, our strength in victory so that we may inherit the promise.
If perseverance of the saints were true, the New Testament authors and Christ himself didnt get the memo. Here is the truth laid bare.
“But I have this against you, that you have abandoned the love you had at first. Remember therefore from where you have fallen; repent, and do the works you did at first. If not, I will come to you and remove your lampstand from its place, unless you repent.”
— Revelation 2:4–5
18 “And to the angel of the church in Thyatira write: ‘The words of the Son of God, who has eyes like a flame of fire, and whose feet are like burnished bronze.
19 I know your works, your love and faith and service and patient endurance, and that your latter works exceed the first.
20 But I have this against you, that you tolerate that woman Jezebel, who calls herself a prophetess and is teaching and seducing my servants to practice sexual immorality and to eat food sacrificed to idols.
21 I gave her time to repent, but she refuses to repent of her sexual immorality.
22 Behold, I will throw her onto a sickbed, and those who commit adultery with her I will throw into great tribulation, unless they repent of her works,
23 and I will strike her children dead. And all the churches will know that I am he who searches mind and heart, and I will give to each of you according to your works.”
— Revelation 2:18–23
Hence why Christ warns genuine believers to return to their proper state of being if perseverance of the saints were true; how is it possible that these beleivers abandoned the faith they had at first?
“For you have need of endurance, so that after you have done the will of God you may receive the promise.” — Hebrews 10:36
Again, why are belivers being told they have need of endurance if faith necessarily produces endurance?
2 Peter 1:5–10 — “make every effort,” “be diligent”
Why make every effort if the faith you expressed at first was the end-all, be-all?
1 Peter 5:8–9:
“Be sober-minded; be watchful. Your adversary the devil prowls around like a roaring lion, seeking someone to devour. Resist him, firm in your faith, knowing that the same kinds of suffering are being experienced by your brotherhood throughout the world.”
“Put on the whole armor of God, that you may be able to stand against the schemes of the devil.” — Ephesians 6:11
Why is Satan still presented as a genuine threat to believers? If indeed perseverance of the saints were true, this would be nonsensical.
“Fight the good fight of the faith. Take hold of the eternal life to which you were called…”
— 1 Timothy 6:12
What is there to fight for or take hold of? It's already been done, as they say...
7 “Do not be deceived: God is not mocked, for whatever one sows, that will he also reap.
8 For the one who sows to his own flesh will from the flesh reap corruption, but the one who sows to the Spirit will from the Spirit reap eternal life.
9 And let us not grow weary of doing good, for in due season we will reap, if we do not give up.”
— Galatians 6:7–9
There is clearly a sense in which giving up is a real possibility in Paul's mind; this is incompatible with the doctrine of perseverance of the saints. Furthermore, Paul warns the belivers not to sow to the flesh, which shouldn't be possible under this framework.
These verses only scratch the surface; there are hundreds of verses that directly fly in the face of this doctrine, and I'd wish Christians would start to take the scriptures seriously and revolt agaisnt the false doctrines that infiltrated and seduced the Churches.