In Romans 2, Paul writes:

He will render to each one according to his works: to those who by patience in well-doing seek for glory and honor and immortality, he will give eternal life; but for those who are self-seeking and do not obey the truth, but obey unrighteousness, there will be wrath and fury. There will be tribulation and distress for every human being who does evil, the Jew first and also the Greek, but glory and honor and peace for everyone who does good, the Jew first and also the Greek. For God shows no partiality.

How can it not be “self-seeking” to “seek for glory and honor and immortality.” Of course the word for “seek” is not actually used the second time. The NASB’s “those who are selfishly ambitious” is better.

Still, how can it be virtuous to pursue glory, honor, and immortality? How is that not selfish?

In the Bible, being “selfish” as we would call it, is actually self-destructive. One is mastered by parts of oneself that one is unable to restrain or control. Thus, selfishness leads to irrational, idiotic behavior that cannot possibly serve one’s best interests.

So God told Cain:

“Why are you angry, and why has your face fallen? If you do well, will you not be accepted? And if you do not do well, sin is crouching at the door. Its desire is for you, but you must rule over it.”

To restrain such influences and impulses in order to pursue a specific goal with endurance and integrity is not selfish because “you” master your “self” rather than the other way around. Cain was mastered by “sin” and thus was one of those who “obey unrighteousness” as a slave to sin.

Romans 6 says that we have died so that we can be free from sin and thus offer our body parts as slaves to righteousness:

For if we have been united with him in a death like his, we shall certainly be united with him in a resurrection like his. We know that our old self was crucified with him in order that the body of sin might be brought to nothing, so that we would no longer be enslaved to sin. For one who has died has been set free from sin. Now if we have died with Christ, we believe that we will also live with him. We know that Christ, being raised from the dead, will never die again; death no longer has dominion over him. For the death he died he died to sin, once for all, but the life he lives he lives to God. So you also must consider yourselves dead to sin and alive to God in Christ Jesus.

Let not sin therefore reign in your mortal body, to make you obey its passions. Do not present your members to sin as instruments for unrighteousness, but present yourselves to God as those who have been brought from death to life, and your members to God as instruments for righteousness. For sin will have no dominion over you, since you are not under law but under grace.

What then? Are we to sin because we are not under law but under grace? By no means! Do you not know that if you present yourselves to anyone as obedient slaves, you are slaves of the one whom you obey, either of sin, which leads to death, or of obedience, which leads to righteousness? But thanks be to God, that you who were once slaves of sin have become obedient from the heart to the standard of teaching to which you were committed, and, having been set free from sin, have become slaves of righteousness. I am speaking in human terms, because of your natural limitations. For just as you once presented your members as slaves to impurity and to lawlessness leading to more lawlessness, so now present your members as slaves to righteousness leading to sanctification.

For when you were slaves of sin, you were free in regard to righteousness. But what fruit were you getting at that time from the things of which you are now ashamed? For the end of those things is death. But now that you have been set free from sin and have become slaves of God, the fruit you get leads to sanctification and its end, eternal life. For the wages of sin is death, but the free gift of God is eternal life in Christ Jesus our Lord.

Notice that this framework is already being set up in Romans 2 with the contrast between those who pursue immortality and glory and those who submit to unrighteousness.