Jesus is man and is God. He is the incarnate Word. He has all authority given to Him as judge and executioner. He is Love, merciful, full of grace, and just.
Don’t mess with His children. Vengeance is His.
In my mind when Jesus starts saying “but whoever”, His tone gets real serious and deep and His eyes show a strong resolve.
Whoever then humbles himself as this child, he is the greatest in the kingdom of heaven. And whoever receives one such child in My name receives Me; but whoever causes one of these little ones who believe in Me to stumble, it would be better for him to have a heavy millstone hung around his neck, and to be drowned in the depth of the sea.
MATTHEW 18:4-6 NASB