Cross reference with Matthew 19:21. What he lacked was not what's needed for salvation (unless you suggest that all must sell all they have and become priests or monks), but what was needed for perfection, i.e., to also store up treasures in heaven, in addition to saving one's soul. He was offering him a higher calling than merely to be personally saved, which he understood him to be looking for, but Jesus knew he wasn't willing to pay the price for that.
"We shall do well to recognize that there are two ways of serving God acceptably - there is the good life required from all religious Christians, and there is the life of perfection to which some, by God's special grace, are called, and which they embrace and fulfill. It was the latter life that Christ put before this young man."
Now you cross reference that with Luke 18:18. All scripture must be interpreted by other scripture. The x-ref in Luke clarifies Matthew. We can see in the x-ref that he wasn't saved because he was lacking. If he was saved, Jesus wouldn't have told him he was lacking what he needed for salvation. He can't be saved in 1 passage but not in the other.
