Paul is very clearly referring to "his ministry" in 1 Cor. 9 when you look at it in context.
It is not for "obtaining eternal life" - Christ already has done that for us in Heb. 9:12
Paul is describing what he does so that he is not disqualified from sharing the gospel which is his ministry.
1 Corinthians 9:18-27 (NASB)
[SUP]18 [/SUP] What then is my reward? That, when I preach the gospel, I may offer the gospel without charge, so as not to make full use of my right in the gospel.
[SUP]19 [/SUP] For though I am free from all men, I have made myself a slave to all, so that I may win more.
[SUP]20 [/SUP] To the Jews I became as a Jew, so that I might win Jews; to those who are under the Law, as under the Law though not being myself under the Law, so that I might win those who are under the Law;
[SUP]21 [/SUP] to those who are without law, as without law, though not being without the law of God but under the law of Christ, so that I might win those who are without law.
[SUP]22 [/SUP] To the weak I became weak, that I might win the weak; I have become all things to all men, so that I may by all means save some.
[SUP]23 [/SUP] I do all things for the sake of the gospel, so that I may become a fellow partaker of it.
[SUP]24 [/SUP] Do you not know that those who run in a race all run, but only one receives the prize? Run in such a way that you may win.
[SUP]25[/SUP] Everyone who competes in the games exercises self-control in all things. They then do it to receive a perishable wreath, but we an imperishable.
[SUP]26 [/SUP] Therefore I run in such a way, as not without aim; I box in such a way, as not beating the air;
[SUP]27[/SUP] but I discipline my body and make it my slave, so that, after I have preached to others, I myself will not be disqualified.
The Father has "qualified us because of Christ " - we don't "qualify ourselves". That is a works-based false gospel.
Colossians 1:12-14 (NASB)
[SUP]12 [/SUP] giving thanks to the Father, who has qualified us to share in the inheritance of the saints in Light.
[SUP]13 [/SUP]
For He rescued us from the domain of darkness, and transferred us to the kingdom of His beloved Son,
[SUP]14 [/SUP] in whom we have redemption, the forgiveness of sins.