A common question. How to respond?
Well let's think about the assumptions underlying the question. If I'm detecting them rightly they go something like this: Faith is an attribute which 'believers' rustle up and which God accepts as payment for heaven. Having accepted the "faith" token from the righteous, God then rewards them with a whole "preferred customers package" of benefits (eternal life, forgiveness, feeling's of love and purpose, etc). Meanwhile, God finds 'unbelievers' lacking in this attribute called faith and so consigns them to this other place called hell.
So the question then comes, How can that be right? And of course, if that's what "God", "faith" and "eternal life"mean, then it isn't right - it's an absurd and capricious set-up which every Christian should repudiate. Thankfully, it's nothing like the gospel.
The gospel is this: God gives us His Son by the Spirit. Christ is Himself eternal life (1 John 5:20). To receive the gift of Christ is what we call faith (John 1:12). To refuse Christ is to resist the Spirit. And it is also, by the very nature of the case, to refuse eternal life.
Therefore God does not sit back and then reward an attribute called "faith" which sinners bring to the table. God actively offers Christ to sinners. As Christ says,
Whoever finds me finds life and obtains favor from the LORD, but he who fails to find me injures himself; all who hate me love death. (Proverbs 8:35-36)