In the aforementioned passage, the apostle Paul is not referring to just any resurrection of the dead, but a resurrection of the dead where the body is:
- “raised in incorruption”1
- “raised in glory”2
- “raised in power”3
- “raised a spiritual body”4
This is also known of the “resurrection of life”5 and “the first resurrection.”6
Before the Lord Jesus Christ died, many people were resurrected from the dead, including Jairus’ daughter7 and Lazarus.8 However, none of them were resurrected in a spiritual, incorruptible, immortal body. Rather, they were resurrected in that same condition they were previously in, possessing a soulish, corruptible, and mortal body. Hence, they were destined to die again.
Is Paul arguing that there is no resurrection if Christ was not raised, and if so, why?
He is arguing that there is no resurrection of the dead unto eternal life if Christ was not raised. First, Christ must have died in order to atone for the sins of humanity. Then, the Holy Spirit had to be given to those who believe in him in order for believers to be spiritually united with Christ.9 In order for the Holy Spirit to be given to all those who believe in him, Christ had to be glorified (by dying and being raised in a glorified body).10
39 But this He spoke concerning the Spirit, whom those believing in Him would receive; for the Holy Spirit was not yet given, because Jesus was not yet glorified. NKJV, ©1982
By being united with Christ, believers “die with” Christ.11 Then, upon the resurrection of the dead unto eternal life, which occurs upon Christ’s return, those Christians still alive can be changed, and those who have died can be resurrected, all unto eternal life, in a spiritual, immortal, and incorruptible body. Only by being “in Christ”—being spiritually united with Christ by means of the indwelling Holy Spirit—is the believer righteous in the eyes of God, and no longer deserving of His wrath.12
21 For He made Him who knew no sin to be sin for us, that we might become the righteousness of God in Him. NKJV, ©1982
The distinction between an ordinary resurrection and a resurrection to eternal life helps, however I wonder whether the Pharisees (and by extension Paul) would have believed in resurrection to eternal life anyway, whether or not this specific person Jesus was raised.
I’d answer affirmatively on account of Daniel 12:2–3.
Perhaps Paul came to realise that Christ's work was a necessary condition for resurrection to eternal life?
The Tanakh is so very limited on details on how one could possibly attain eternal life, especially by means of the resurrection of (from) the dead. What life the Torah offers for absolute perfect obedience to the commandments is merely prolonged life upon earth during one’s first life (so to speak). What the apostle Paul propounded in his epistles, I surmise that such intricate knowledge must have come from God, as it is difficult to fathom how it could be derived literally (by a gross reading) from the Tanakh.
Before knowing Christ might he have believed in resurrection to eternal life but not known about Christ as a necessary condition?
Again, since Daniel speaks of a resurrection to eternal life, the apostle Paul would certainly have believed in it. But, the mechanics and the process of attaining that eternal life via the resurrection was a mystery.
1 1 Cor. 15:42
2 1 Cor. 15:43
4 1 Cor. 15:44
5 John 5:29 cf. Dan. 12:2
6 Rev. 20:4–6
7 Mar. 5:22–43
8 John 11:44
9 1 Cor. 6:17 cf. 1 Cor. 12:13
10 John 7:39
11 Rom. 6:8 cf. 2 Tim. 2:11; Rom. 6:3, 7:4
12 2 Cor. 5:21