Earthly life is precious because (1) it was created by God; (2) God declared it "very good"; (3) God is on the side of life over death; (4) Jesus' earthly ministry was largely one of healing and saving physical lives; (5) God loves the "world" in the sense of mankind in general, and Jesus died for this world.
Then God said, "Let us make man in our image, after our likeness; and let them have dominion ..... So God created man in his own image, in the image of God he created him; male and female he created them. And God blessed them, and God said to them, "Be fruitful and multiply, and fill the earth and subdue it; and have dominion over the fish of the sea and over the birds of the air and over every living thing that moves upon the earth." ... And God say everything that he had made, and behold, it was very good.
--Genesis 1: 26-31 RSV
I [Moses] call heaven and earth to witness against you this day, that I have set before you life and death, blessing and curse; therefore choose life, that you and your descendants may life, loving the Lord your God, obeying his voice, and cleaving to him; for that means life to you and length of days, that you may dwell in the land which the Lord swore to your fathers, to Abraham, to Isaac, and to Jacob, to give them.
-- Deuteronomy 30:19-20 RSV
And Jesus went about all the cities and villages, teaching in their synagogues and preaching the gospel of the kingdom, and healing every disease and every infirmity. When he saw the crowds, he had compassion on them, because they were harassed and helpless, like sheep without a shepherd.
Matthew 9:35-36 RSV
"Are not two sparrows sold for a penny? And not one of them will fall to the ground without your Father's will. But even the hairs of your head are all numbered. Fear not, therefore; you are of more value than many sparrows."
Matthew 10:29-30 RSV
Put on then, as God's chosen ones, holy and beloved, compassion, kindness, lowliness, meekness, and patience, forbearing one another and, if one has a complaint against another, forgiving each other; as the Lord has forgiven you, so also you must forgive. And above all these put on love, which binds everything together in perfect harmony. And let the peace of Christ dwell in your hearts....
Colossians 3:12-15