Only those who are saved/believers are in the light.
Acts 26:18 - to open their eyes, in order to turn them from darkness to light, and from the power of Satan to God, that they may receive forgiveness of sins and an inheritance among those who are sanctified by faith in Me.
I notice how it says "to turn" people "from the power of Satan to God". So, Satan's children are in his power. And our Apostle Paul in Ephesians 2:2 says there is >
"the spirit who now works in the sons of disobedience." (in Ephesians 2:2)
And elsewhere he has said we in sin were slaves of sin . . . not free. Adam and Eve's wills were free before they fell. They lost their freedom, when they fell to Satan and his evil spirit > Ephesians 2:2. And now we see how people are being worked-in by Satan's evil spirit . . . of selfishness. Their evil nature is dictating the choices they make, and what they are thinking and how they are reacting and being driven by dominating and dictatorial demands for pleasure.
Our true character has a lot to do with what we are capable of choosing. Jesus says, "without Me you can do nothing," in John 15:5.
So, only in Jesus are we capable of choosing what is really good >
"for it is God who works in you both to will and to do for His good pleasure." (Philippians 2:13)
Of ourselves, we are not good; only God is good. Only God in us can have us willing and doing what is good. And He is almighty to keep us with Him. We do not have the sufficiency to keep ourselves willing and not failing. "My grace is sufficient for you," Jesus says in 2 Corinthians 12:9. So we depend on Him.
But are we perfectly incapable of sinning? Paul told the Philippians how they had increased in their obedience, even while Paul was absent > Philippians 2:12. Why did their obedience increase? Because "God gave the increase." (in Corinthians 3:6) Because, as he says in the next verse, God is the One working in our willing and doing > Philippians 2:13. He works in our wills so our obedience is increasing.
Even so, can we do wrong things and be the wrong way? Can we become unforgiving, can we become dominating and controlling of other people, can we get nasty at someone instead of first caring for the person in prayer to bless the person? Can we argue or complain? Can we worry and fear (1 John 4:17-18, Philippians 4:6-7? Can our attention get away from staying submissive to how our Father rules us with His own peace in our "hearts"? (Colossians 3:15)
Paul says,
"Do all things without complaining and disputing, that you may become blameless and harmless, children of God without fault in the midst of a crooked and perverse generation," (in Philippians 2:13-16)
Paul says to stop complaining and arguing, so that we "may become" "without fault". He says this to the Philippians who he just said have increased in their obedience because of God's working in their wills. And yet it looks like they still needed to become "without fault". So, from this I can see how we can be with God in us, but we still need more correction against how we still can sin because of our faults.
Plus, Hebrews 12:4-14 guarantees how every child of God gets our Heavenly Father's correction. We don't need correction if we are without sin, I would say. Also, we see what are the guaranteed results of God's correction > we share in His own holiness, in the "peaceable fruit of righteousness" of His love. This is the guaranteed result of God's correction changing our nature to be like Jesus and God's love. From this, I see how if we have trusted in Jesus, we are guaranteed how God will keep us plus change us with real correction so we are "conformed to the image of His Son, that He might be the firstborn among many brethren." (in Romans 8:29)
We have trusted Him for all He is able to do. So, we are not left to fail in our human will which is not good like God.