Here "in" I suggest does not mean incorporated into Himself as He is light and there is no darkness in Him. However darkness is still in His hand.John 3:35. "in Him all things hold together" suggests to me that all things are in His plan rather the outcome of all things are in His plan. I say this because Col 1:17 seems to go beyond God allowing evil and then making good come from it. "in Him all things hold together" suggests to me that the Devil's thoughts, actions and words are given to him, rather than created by him out of nothing by his own power. God is holy and this is not effected by His having created that which is other than Himself. What considerations are relevant to deciding what "in" means in, "in Him all things hold together"? E.S.V. "And he is before all things, and in him all things hold together".
The King James Bible reads: "And he is before all things, and by him all things consist."
The meaning is, that they are kept in the present state; their existence, order, and arrangement are continued by his power. If unsupported by him, they would fall into disorder, or sink back to nothing. If this be the proper interpretation, then it is the ascription to Christ of infinite power - for nothing less could be sufficient to uphold the universe; and of infinite wisdom - for this is needed to preserve the harmonious action of the suns and systems of which it is composed. None could do this but one who is divine; and hence we see the reason why he is represented as the image of the invisible God. He is the great and glorious and everactive agent by whom the perfections of God are made known.