Actually, it is Paul who assumes it,
which is why he would rather die on the spot than continue living:
"I desire to depart and be with Christ which is better by far, but it is more necessary for you that I remain in the body." (Php 1:23-24)
You're grasping, Butch.
The Scriptures are clear that the human spirit is immortal.
As I said, If you look at what the Pharisees believed you'd see what Paul believed. He says nothing about immediately being with Christ, that's an assumption. One only assumes that if they already believe there is a part of man that lives on after death. the passage says nothing about a man living on after death. The Scriptures don't teach that, that is an inference that is drawn from certain passages, however, it is draw based on preconceptions, not the teaching of Scripture.
If we look at what the Scriptures do teach about what a man is we can look at the creation account.
7 And the LORD
God formed man of the dust of the ground, and breathed into his nostrils the breath of life; and man became a living being. (Gen 2:7 NKJ)
Man was formed from the dust of the ground. God then breathed the breath/spirit of life into the man and the man became something else, he became a living soul. According to this passage a living soul consists of two things, the breath/spirit of life and a body (man). God told Adam if he ate from the tree of the knowledge of good and evil he would die. He told him that he would return to the dust. In Ecclesiastes we find that the body returns to the dust and the breath/spirit returns to God. We learned from Gen.2 that that breath/spirit is God's. In Ezekiel 37 God give a picture of the resurrection by bringing the bones together and putting flesh on them and says this.
11 Then He said to me, "Son of man, these bones are the whole house of Israel. They indeed say,`Our bones are dry, our hope is lost, and we ourselves are cut off!'
12 "Therefore prophesy and say to them,`Thus says the Lord GOD: "Behold, O My people, I will open your graves and cause you to come up from your graves, and bring you into the land of Israel.
13 "Then you shall know that I am the LORD, when I have opened your graves, O My people, and brought you up from your graves.
14
"I will put My Spirit in you, and you shall live, and I will place you in your own land. Then you shall know that I, the LORD, have spoken it and performed it," says the LORD.'" (Eze 37:11-14 NKJ)
Notice whose spirit it is that makes them live. God said, " I will put MY Spirit in you". It is God's breath/spirit that gives man life not his own. Man is flesh and bone not spirit. Jesus said the same thing to the apostles when they thought they had seen a spirit.
37 But they were terrified and frightened, and supposed they had seen a spirit.
38 And He said to them, "Why are you troubled? And why do doubts arise in your hearts?
39 "Behold My hands and My feet, that it is I Myself. Handle Me and see,
for a spirit does not have flesh and bones as you see I have." (Luk 24:37-39 NKJ)
He said a spirit does not have flesh and bones. If you have flesh and bones you are not a spirit.