John Calvin is a heavenly minded man, and throughout the institutes, he pessimistic about the number of people who will be saved. The Reformation was a great revival but the few Reformed city-states that existed were Geneva, Strasbourg, Zurich and a few spurious others, and their sum population was nothing in relationship to the global population of the 16th century. In an unexpected place, among Calvin's famous excursion on the Lord's Prayer, he reveals a very optimistic eschatology! THY KINGDOM COME in Institutes III.20.41-41 explains that the Kingdom of God will advance until the second coming of Christ, and all of his enemies will be conquered and all of the saints will be sanctified in an increasing trajectory until the very end where the whole human race will reverence Christ the Lord. Optimistic Eschatologies like Post-Millennialism became vogue in the following centuries among the best Reformed Theologians, culminating (or rather ending) in the World Wars.

The bold print has been added to emphasis some of the interesting statements by John Calvin, in this key section of the Institutes, to provide insight into this illustrious reformer's own eschatology: 

Institutes Book III.20.41

41. The first petition is, HALLOWED BE THY NAME. The necessity of presenting it bespeaks our great disgrace. For what can be more unbecoming than that our ingratitude and malice should impair, our audacity and petulance should as much as in them lies destroy, the glory of God? But though all the ungodly should burst with sacrilegious rage, the holiness of God’s name still shines forth. Justly does the Psalmist exclaim, “According to thy name, O God, so is thy praise unto the ends of the earth,” (Ps. 48:10). For wherever God hath made himself known, his perfections must be displayed, his power, goodness, wisdom, justice, mercy, and truth, which fill us with admiration, and incite us to show forth his praise. Therefore, as the name of God is not duly hallowed on the earth, and we are otherwise unable to assert it, it is at least our duty to make it the subject of our prayers.

The sum of the whole is, It must be our desire that God may receive the honour which is his due: that men may never think or speak of him without the greatest reverence. The opposite of this reverence is profanity, which has always been too common in the world, and is very prevalent in the present day. Hence the necessity of the petition, which, if piety had any proper existence among us, would be superfluous. But if the name of God is duly hallowed only when separated from all other names it alone is glorified, we are in the petition enjoined to ask not only that God would vindicate his sacred name from all contempt and insult, but also that he would compel the whole human race (humanum genus) to reverence it.

Then since God manifests himself to us partly by his word, and partly by his works, he is not sanctified unless in regard to both of these we ascribe to him what is due, and thus embrace whatever has proceeded from him, giving no less praise to his justice than to his mercy. On the manifold diversity of his works he has inscribed the marks of his glory, and these ought to call forth from every tongue an ascription of praise. Thus Scripture will obtain its due authority with us, and no event will hinder us from celebrating the praises of God, in regard to every part of his government. On the other hand, the petition implies a wish that all impiety which pollutes this sacred name may perish and be extinguished, that every thing which obscures or impairs his glory, all detraction and insult, may cease; that all blasphemy being suppressed, the divine majesty may be more and more signally displayed.

Institutes Book III.20.42

The second petition is, THY KINGDOM COME (Matt 6:10). This contains nothing new, and yet there is good reason for distinguishing it from the first. For if we consider our lethargy in the greatest of all matters, we shall see how necessary it is that what ought to be in itself perfectly known should be inculcated at greater length. Therefore, after the injunction to pray that God would reduce to order, and at length completely efface every stain which is thrown on his sacred name, another petition, containing almost the same wish, is added--viz. Thy kingdom come. (Matt 6:10)

Although a definition of this kingdom has already been given, I now briefly repeat that God reigns when men, in denial of themselves and contempt of the world and this earthly life, devote themselves to righteousness and aspire to heaven (see Calvin, Harm. Mt. 6) Thus this kingdom consists of two parts; the first is, when God by the agency of his Spirit corrects all the depraved lusts of the flesh, which in bands war against Him; and the second, when he brings all our thoughts into obedience to his authority.

This petition, therefore, is duly presented only by those who begin with themselves; in other words, who pray that they may be purified from all the corruptions which disturb the tranquility and impair the purity of God’s kingdom. Then as the word of God is like his royal scepter, we are here enjoined to pray that he would subdue all minds and hearts to voluntary obedience. This is done when by the secret inspiration of his Spirit he displays the efficacy of his word, and raises it to the place of honour which it deserves. We must next descend to the wicked, who perversely and with desperate madness resist his authority. God, therefore, sets up his kingdom, by humbling the whole world, though in different ways, taming the wantonness of some, and breaking the ungovernable pride of others. We should desire this to be done every day, in order that God may gather churches to himself from all quarters of the world, may extend and increase their numbers, enrich them with his gifts, establish due order among them; on the other hand, beat down all the enemies of pure doctrine and religion, dissipate their counsels, defeat their attempts. Hence it appears that there is good ground for the precept which enjoins daily progress, for human affairs are never so prosperous as when the impurities of vice are purged away, and integrity flourishes in full vigor. The completion, however, is deferred to the final advent of Christ, when, as Paul declares, "God will be all in all," (1 Cor 15:28).

This prayer, therefore, ought to withdraw us from the corruptions of the world which separate us from God, and prevent his kingdom from flourishing within us; secondly, it ought to inflame us with an ardent desire for the mortification of the flesh; and, lastly, it ought to train us to the endurance of the cross; since this is the way in which God would have his kingdom to be advanced. It ought not to grieve us that the outward man decays provided the inner man is renewed. For such is the nature of the kingdom of God, that while we submit to his righteousness he makes us partakers of his glory. This is the case when continually adding to his light and truth, by which the lies and the darkness of Satan and his kingdom are dissipated, extinguished, and destroyed, he protects his people, guides them aright by the agency of his Spirit, and confirms them in perseverance; while, on the other hand, he frustrates the impious conspiracies of his enemies, dissipates their wiles and frauds, prevents their malice and curbs their petulance, until at length he consume Antichrist "with the spirit of his mouth," and destroy all impiety "with the brightness of his coming," (2 Thess 2:8, Calv Com). 

See Calvin's Commentaries on Ps 2:8, 21:8, 28:4, 45:16, 47:8, 72:8, 110:2; Matt 6:10; 12:31; John 13:31f