It appears that you're not grasping the full context or...

It appears that you're not grasping the full context or interpretation of this verse and that can easily be done, if we go on our first gut instinct.

For what I read of a number of passages (the whole theme), the firstborn of God's inner creations, where our creations begin, was for a Jesus to be, born from Mary.
Hence for in him = for this reason, for the one to be, all things were created, through, on account of, by reason of, for the sake of him, the one to be = the meaning of the words in that verse -> "created in Christ Jesus".

The following part, falls upon us, but we are to follow in Jesus's footsteps, so to speak -> "unto good works, which God hath before ordained that we should walk in them."

John 17:4 - I have glorified thee on the earth: I have finished the work which thou gavest me to do.

The latter of that verse, as numerous verses also show = predestination or at least, hints of.
Where it has the word "should", the Interlinear says that should not be there, just -> ",that in them we walk".