Life flows from God. Thus, its intrinsic value revolves around the Creator. In other words, without God there’s no substance to life.
And the only way for life’s meaning to materialize is to love and serve God by loving and serving one another.
“‘Love the Lord your God with all your heart and with all your soul and with all your mind.‘ This is the first and greatest commandment. And the second is like it: ‘Love your neighbor as yourself.’ All the Law and the Prophets hang on these two commandments.” Matthew 22:37-40
“Whoever wants to be great among you, let him be one who serves.” Matthew 20:26
When you buy a car, for instance, you buy something that was created to serve the one who buys it. Likewise, God created us to love and serve.
If there’s any other lopsided disposition in the human soul, then the heart has become adversely infected and is in dire need of an adjustment.
“Above all else, guard your heart, for everything you do flows from it.” Proverbs 4:23
As to why we toil under the sun, please read To Infinity and Beyond.