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".
