It is well-known that much of American evangelicalism holds the idea that if God provides some form of grace (say, salvation) to one person, he is really obliged to provide it equally to everybody. That's not a biblical concept (Rom. 9:15, for example), but it is still widely held in society. Where did it come from?
Maybe our kindergarten teachers taught it to us. You remember the little book that was popular back in the 90s, called, Everything I Needed to Know, I Learned in Kindergarten? I thought the book was a dumb idea then, because it isn't true, and if it contributed to our theological mess, I think it is even dumber now than I did then. It was cute, but still dumb.
Pretty much everyone I know has had some form of this experience- "I brought a piece of candy to school...the teacher saw it and said, 'If you don't have enough of those for everybody, you can't have any either!' So I put it away (or had it confiscated)." Is that where we got this misguided idea about God?
R. C. Sproul, in his classic book, The Holiness of God, addresses it this way-
It is impossible for anyone, anywhere, anytime to deserve grace. Grace by definition is undeserved. As soon as we talk about deserving something, we are no longer talking about grace; we are talking about justice. Only justice can be deserved. God is never obligated to be merciful. Mercy and grace must be voluntary or they are no longer mercy and grace. God never “owes” grace. He reminds us more than once. “I will have mercy on whom I will have mercy.” This is the divine prerogative. God reserves for Himself the supreme right of executive clemency.
Suppose ten people sin and sin equally. Suppose God punishes five of them and is merciful to the other five. Is this injustice? No! In this situation five people get justice and five get mercy. No one gets injustice. What we tend to assume is this: If God is merciful to five He must be equally merciful to the other five. Why? He is never obligated to be merciful. If He is merciful to nine of the ten, the tenth cannot complain that he is a victim of injustice. God never owes mercy. God is not obliged to treat all men equally. Maybe I’d better say that again. God is never obliged to treat all men equally. If He were ever unjust to us, we would have reason to complain. But simply because He grants mercy to my neighbor gives me no claim on His mercy. Again we must remember that mercy is always voluntary. “I will have mercy upon whom I will have mercy.” (p. 128-9)
By the way, if we are indeed getting some of our ideas about God from secular schooling and the control of interpersonal behavior therein, that does not paint a pretty picture of theological education in our churches.
Get this book by Sproul. If you live near me, ask me and I'll give you a copy. It's worth the read.