To be in God's hand means also that if we should fall he will guide us back to him. He chastises those he loves. And I think that is the point perhaps.
True. But the chastisement of the Lord is not suffering the effects of sin in this life, which is common for all sinners 'the morning after'.
The Lord's chastisement for sinning with the devil, is having no fellowship with Him and being separated from His life and grace, which is the wage for every soul that sins.
The Lord will not engage in respect of persons with His own people, by continuing to have fellowship with His people, while sinning against Him.
Only the sons of God can know what it is to now be without fellowship with the Father, by sinning against Him, because the world live that way naturally.
No one misses what they have never known. Only the sons of God can miss fellowship with God, because they now have none do to sinning.
My little children, these things write I unto you, that ye sin not. And if any man sin, we have an advocate with the Father, Jesus Christ the righteous: And he is the propitiation for our sins: and not for ours only, but also for the sins of the whole world.
This Scripture speaks of
any man without respect of persons, whether confessing Christian, Jew, Muslim, Buddhist, or atheist.
If any man is sinning against God, there is no fellowship with Jesus in the Light, but are walking in darkness as any other sinner of the world. So that if we are sinning we are cut off from the true Light in Christ Jesus, and unless we confess with godly sorrow, we will continue in that darkness.
The Lord's chastisement is to let His own people go back into darkness, if they persist in despising the Spirit of His grace not to do so.
The Lord cannot chastise the world, as His own people, because the world doesn't even know what having true fellowship with Jesus Christ is in the first place.
Before I was born again, I never knew the fellowship of Light and peace and righteousness in the Spirit of Christ. Now I do. And if I sin like any other sinners without God, then I will know the separation and deadness of soul without Him.