It’s true that having a sense of purpose and self-sacrifice gives our life meaning.
From the book Life Is in the Transitions: Mastering Change at Any Age:
Having a cause–a thee story–is the third great pillar in living a meaningful life. A cause is something you believe in that’s bigger than yourself. It’s serving God, being green, mentoring, marching, caretaking, canvassing. Supporting a cause gives you a sense of purpose and self-sacrifice. And it’s good for you: Those who volunteer enjoy higher levels of happiness and live longer.
But I’d rather say that there is a kind of purpose that gives us a fulfillment that lasts.
And what is it?
To become the human we are supposed to be.
And how to do it?
By being like Christ.
Philippians 2:1-18 AMP
1 Therefore if there is any encouragement and comfort in Christ [as there certainly is in abundance], if there is any consolation of love, if there is any fellowship [that we share] in the Spirit, if [there is] any [great depth of] affection and compassion,
2 make my joy complete by being of the same mind, having the same lovea [toward one another], knit together in spirit, intent on one purpose [and living a life that reflects your faith and spreads the gospel—the good news regarding salvation through faith in Christ].
3 Do nothing from selfishness or empty conceit [through factional motives, or strife], but with [an attitude of] humility [being neither arrogant nor self-righteous], regard others as more important than yourselves.
4 Do not merely look out for your own personal interests, but also for the interests of others.
5 Have this same attitude in yourselves which was in Christ Jesus [look to Him as your example in selfless humility],
6 who, although He existed in the form and unchanging essence of God [as One with Him, possessing the fullness of all the divine attributes—the entire nature of deity], did not regard equality with God a thing to be grasped or asserted [as if He did not already possess it, or was afraid of losing it];
7 but emptied Himself [without renouncing or diminishing His deity, but only temporarily giving up the outward expression of divine equality and His rightful dignity] by assuming the form of a bond-servant, and being made in the likeness of men [He became completely human but was without sin, being fully God and fully man].
8 After He was found in [terms of His] outward appearance as a man [for a divinely-appointed time], He humbled Himself [still further] by becoming obedient [to the Father] to the point of death, even death on a cross.
9 For this reason also [because He obeyed and so completely humbled Himself], God has highly exalted Him and bestowed on Him the name which is above every name,
10 so that at the name of Jesus EVERY KNEE SHALL BOWb [in submission], of those who are in heaven and on earth and under the earth,
11 and that every tongue will confess and openly acknowledge that Jesus Christ is Lord (sovereign God), to the glory of God the Father.
12 So then, my dear ones, just as you have always obeyed [my instructions with enthusiasm], not only in my presence, but now much more in my absence, continue to work out your salvation [that is, cultivate it, bring it to full effect, actively pursue spiritual maturity] with awe-inspired fear and trembling [using serious caution and critical self-evaluation to avoid anything that might offend God or discredit the name of Christ].
13 For it is [not your strength, but it is] God who is effectively at work in youc, both to will and to work [that is, strengthening, energizing, and creating in you the longing and the ability to fulfill your purpose] for His good pleasure.
14 Do everything without murmuring or questioning [the providence of God],
15 so that you may prove yourselves to be blameless and guileless, innocent and uncontaminated, children of God without blemish in the midst of a [morally] crooked and [spiritually] perverted generation, among whom you are seen as bright lights [beacons shining out clearly] in the world [of darkness],
16 holding out and offering to everyone the word of life, so that in the day of Christ I will have reason to rejoice greatly because I did not run [my race] in vain nor labor without result.
17 But even if I am being poured out as a drink offeringd on the sacrifice and service of your faith [for preaching the message of salvation], still I rejoice and share my joy with you all.
18 You too, rejoice in the same way and share your joy with me.
Footnotes from Amplified Bible:
a love — The key to understanding this and other statements about love is to know that this love (the Greek word agape) is not so much a matter of emotion as it is of doing things for the benefit of another person, that is, having an unselfish concern for another and a willingness to seek the best for another.
b EVERY KNEE SHALL BOW — All intelligent beings in the universe, whether saved or unsaved, whether in spirit or as mortal mankind, will acknowledge Him.
c God who is effectively at work in you — God supports the believer, but it is the believer’s responsibility to do what he has been called by God to do.
d drink offering — The drink offering (wine) was required as part of the sacrificial system of the old covenant.