Because this question invites a longer-than-usual answer, this blog will be divided into three installments. Part of the point of blogs is that they’re not supposed to be too long!
The first installment asks whether rewards are compatible with grace (an issue revisited at points also in the later installments). Contrary to what we might think, rewards are not antithetical to grace. It also shows that the point of the language of reward is not about boasting. The second, more important and somewhat longer installment (http://www.craigkeener.com/rewards-part-ii-what-were-rewarded-for/) will address what we’re rewarded for. The third installment (http://www.craigkeener.com/rewards-part-iii-what-the-reward-is/) extrapolates from some biblical teaching to try to understand what the reward is.
Rewards versus grace?
Grace isn’t fair; happily, it’s more generous than fair, since by fairness we would all be punished for our offenses against an infinitely holy God. Not all are converted and thus enrolled in God’s service at the same time. Grace means that those paid (or “rewarded”) for one hour of work get the same pay (i.e., the kingdom) as those who worked all day (Matt 20:12-16). (The term for “wages” in 20:8 also means “reward.”) We can all be glad that grace isn’t fair, because God’s grace is better than fair. It means that we can be saved even though we don’t deserve it. Some passages in the Bible may speak of salvation as the “reward” of perseverance (see Heb 10:35-39).
But often the Bible speaks of other rewards. Grace isn’t fair, but God is also a God of justice, so people’s true works will also be exposed, whether good or bad (Rom 2:6-11; 2 Cor 5:10; Revelation 22:12). Those who depend solely on themselves and have not accepted God’s grace will be punished for their sins, though some will be more accountable than others (cf. Luke 12:46-48; Rom 2:12).
Those who embrace grace will not be condemned for their sins, but the day of judgment will publicly reveal reality without our current filters. In light of eternity, Paul says, our hearts will be laid bare, even our motives revealed (1 Cor 4:5). We may try to keep them hidden from others now, but they will all come to light someday. God knows what we really are, so we should seek to become what he wants us to be. The emptiness of life without God will be revealed and bring him glory, but he will get the greatest glory from those devoted to his honor.
Reward isn’t about boasting
Rewards themselves are a matter of grace, since it’s only God’s kindness toward us that makes us right with him to begin with. Rewards are just, but the greatest rewards are for the most perfect righteousness—which is the fruit of his own grace within us (Gal 5:22-23). Rewards are just, but God’s standard of justice is perfect because he alone knows each person’s heart and circumstances. Nobody else can predict these matters in advance.
In 1 Corinthians 3:4-23, Paul challenges the Corinthian predilection to revere Christian celebrities; some exalt Paul, whereas others prefer Apollos. Paul warns them that they are using immature, worldly standards (3:1-4). The day of judgment will reveal who is really building on the foundation of Christ, and we can’t really know that outcome until then (3:10-15, esp. 3:13). (Indeed, Paul says, he doesn’t even try to evaluate his own status that way—1 Cor 4:3.)
Even if we know the person well enough to trust their basic sincerity, we don’t know the depths of their hearts; only God does. We don’t know what a person has had to overcome to get to where they are. We don’t know how sincerely they are working for Christ. If we think of heavenly rewards in terms of worldly competition, we precisely miss Paul’s point in the context: the point is that we shouldn’t compete or seek our own (or our “heroes’”) honor (3:3-4). The purpose of Christian leaders is to serve God’s people as a whole, who should be the eternal organ of God’s glory (3:16-23).
Precisely because it is God who works through any of us (1 Cor 3:5-9), we shouldn’t boast in how God uses us. (Thanking God for what he’s doing is not boasting in ourselves; it’s all right for us to brag about God himself, so long as our motive is his honor and not ours.) “Gifts” are not something that we earn (4:7); indeed, Paul’s term that we often translate “gift”—charisma—in 1:7 and 12:4-31 (compare also 7:7), is something that comes by charis, that is, by grace, by God’s generous kindness. So God doesn’t evaluate us by how great our gifts are, but by what we do with them—by our motives of love. Rather than boasting in our gifts, we should use whatever they are for God’s glory, seeking with all our heart for him to be honored.
What God evaluates as great differs from human judgment (1 Sam 16:7). He’s near the broken and lowly, but far from the proud (Ps 138:6; Prov 3:34; James 4:6; 1 Pet 5:5). That’s why Hannah compares favorably to the chief priest Eli in 1 Samuel 1. That’s also why Mary, a lowly village teenager, is more highly favored than the priest Zechariah in Luke 1 (although Zechariah is godly and blessed also). To the eyes of contemporaries, Mary had no prominent or important role like a priest or prophet; but God favored her with raising the Messiah. God scattered the proud but exalted the humble (Luke 1:48, 51-53), showing that he is not impressed by human power, fame, education or wealth.
God will reward our labors for him, but God who alone knows the hearts knows best what our labors really entail. All is by grace, even the power for us to labor for him (Col 1:29).