We need Jesus Christ in us because, as Paul writes in Romans 5:12, "... death has spread to the whole human race because everynoe has sinned."
Not a one of us escapes sinning except we come to Jesus Christ and live in him. Through him alone can we die to sin and overcome our slavery to it.
What I just wrote seems analogous to the Israelites after being led out of Egypt, freed from slavery, yet wanting to go back to Egypt because their journey in the desert was difficult and not anything they expected it would be. What I wrote prompted the thought of people who come to Christ and believe themselves to be Christian, but will or want to go back to their state of enslavement to the material world because being Christian is too hard to maintain, or it isn't what they expected it was going to be. I can think of a parable with that theme: The Sower, Matthew 13:4.