Few men stared as deeply into the glories of eternal life as Jonathan Edwards.  In a sermon on Romans 2:10 ("But glory, honor and peace for everyone who does good: first for the Jew, then for the Gentile") he preached on why there will be different levels of reward in heaven, why those at the lower levels will never be envious of those above them, and how the saints in heaven can praise God continually throughout eternity without ever growing tired.   

"As there are degrees among the angels, viz. thrones, dominions, principalities, and powers; so there are degrees among the saints. In heaven are many mansions, and of different degrees of dignity. The glory of the saints above will be in some proportion to their eminency in holiness and good works here. Christ will reward all according to their works. He that gained ten pounds was made ruler over ten cities, and he that gained five pounds over five cities. Luke 19:17; 2 Cor. 9:6, "He that soweth sparingly, shall reap sparingly; and he that soweth bountifully shall reap also bountifully." And the apostle Paul tells us that, as one star differs from another star in glory, so also it shall be in the resurrection of the dead. 1 Cor. 15:41.   

"Christ tells us that he who gives a cup of cold water unto a disciple in the name of a disciple, shall in no wise lose his reward. But this could not be true, if a person should have no greater reward for doing many good works than if he did but few.  

"It will be no damp to the happiness of those who have lower degrees of happiness and glory, that there are others advanced in glory above them. For all shall be perfectly happy, every one shall be perfectly satisfied. Every vessel that is cast into this ocean of happiness is full, though there are some vessels far larger than others. And there shall be no such thing as envy in heaven, but perfect love shall reign through the whole society. Those who are not so high in glory as other, will not envy those that are higher, but they will have so great, and strong, and pure love to them, that they will rejoice in their superior happiness. Their love to them will be such that they will rejoice that they are happier than themselves; so that instead of having a damp to their own happiness, it will add to it. They will see it to be fit that they that have been most eminent in works of righteousness should be most highly exalted in glory. And they will rejoice in having that done, that is fittest to be done. 

"There will be a perfect harmony in that society; those that are most happy will also be most holy, and all will be both perfectly holy and perfectly happy. But yet there will be different degrees of both holiness and happiness according to the measure of each one's capacity, and therefore those that are lowest in glory will have the greatest love to those that are highest in happiness, because they will see most of the image of God in them. And having the greatest love to them, they will rejoice to see them the most happy and the highest in glory. And so, on the other hand, those that are highest in glory, as they will be the most lovely, so they will be fullest of love. As they will excel in happiness, they will proportionally excel in divine benevolence and love to others, and will have more love to God and to the saints than those that are lower in holiness and happiness. And besides, those that will excel in glory will also excel in humility...

"This happiness of the saints shall never have any interruption.  There will never be any alloy to it; there never will come any cloud to obscure their light; there never will be any thing to cool their love.  The rivers of pleasure will not fail, the glory and love of God and of Christ will for ever be the same, and the manifestation of it will have no interruption.  No sin or corruption shall ever enter there, no temptation to distrub their blessedness; the divine love in the saints shall never cool, there shall be no incosistency in any of them, the faculties of the saints shall never flag from exercise; and they will never be cloyed, their relish for those delights will for ever be kept up to its height, that glorious society shall not grow weary of their hallelujahs.  Their exercises, though they are so active and vigorous, will be performed with perfect ease; the saints shall not be weary of loving, and praising, and fearing, as the sun is never weary of shining."  Jonathan Edwards, The Works of Jonathan Edwards, volume 2, p. 902.