Why should any person try to be good if everyone in the world is bound for heaven regardless?
I suppose this question weighs heavily on the minds of many because the answer cannot be reasoned to. No argument, no proof can convince a man to be good for the sake of good; he must intuit it. It’s the same as when a crooked man asks why he should be faithful to his wife. “Because she loves you and will never leave you,” the honest man replies. “Exactly,” says the crooked man, “she loves me and will never leave me. I don’t need to be faithful.” You ask why be good if everyone goes to heaven. I ask why be good otherwise.
This brings me to a larger concern. I worry that too many Christians resemble the Older Son in the Parable of the Prodigal Son. Too many hear the music and dancing, are told that the Father’s lost children will be found, and refuse to celebrate. They reject the Good News! God is more generous than they ever imagined, so they grumble, or worse, they get angry. The Parable of the Laborers in the Vineyard speaks to this condition of the heart as well. And Jesus’ conclusion is startling. “The last will be first, and the first last.” (Matthew 20:16)
Having said that, I can give you the Biblical reasons for being good, and I hope you see the truth of them.
First, God commands us to be good -- “You therefore must be perfect, as your heavenly Father is perfect.” (Matthew 5:48) We are called to imitate God since He made us in His image, and God is good. Second, our obedience to this command should be out of love. (John 14:15) Anything else -- hope of reward, fear of punishment -- is not perfect love for the Father. Certainly, the number of people in Heaven (whether few or many or all) should have no bearing on being good.