The book is outlined as an exposition of the Apostles' Creed, and is organized by explanations of God the Creator, God the Redeemer, God the Sanctifier, and the Holy Catholic Church.
While there are countless subjects which he expands on, I will comment on five that really shaped me:
Idolatry
"... whenever [Scripture's] object is to discriminate between the true God and false deities, it opposes him in particular to idols; not that it approves of what is taught more elegantly and subtly by philosophers, but that it may the better expose the folly, no, madness of the world and its inquiries after God, so long as everyone clings to his own speculations. This exclusive definition, which we uniformly meet with in Scripture, annihilates every deity which men frame for themselves of their own accord-God himself being the only fit witness to himself" (Book I. Ch 11.1) .
Calvin presents an extremely holistic view of humanity through this lens of idolatry. There are those who are without the revelation of the true, living God in Jesus Christ as witnessed in Scripture and those who create their own gods. The default human position apart from this revelation is idolatry: "the human mind is, so to speak, a perpetual forge of idols."
Faith
His discussion on faith is the basic framework for what Edwards presents in Religious Affections, namely, that "happen what may, faith ceases not to long after God" (Book III. Ch 2.24). Just like Edwards, Calvin linked true faith to real affection for Christ as he is revealed in the word:
"There is an inseparable relation between faith and the word, and that these can no more be disconnected from each other than rays of light from the sun" (Book III. Ch 2.6).
"Faith consists in the knowledge of Christ; Christ cannot be known without the sanctification of his Spirit: therefore faith cannot possibly be disjoined from pious affection" (Book III. Ch 2.8)
Meditating on the Future Life
One smaller part of the book that is quite profound is his discourse on the future life. Humanity has become so fascinated with the temporal things around them - all of which are finite and slipping away: "... we form all our plans just as if we had fixed our immortality on the earth" (Book III. Ch 9.2). He calls the Christian to wake up to the reality of this fading world and live in the light of the eternal world to come. He understands this present life as perpetual exile: "If we reflect that by death we are recalled from exile to inhabit our native country, a heavenly country, shall this give us no comfort? But everything longs for permanent existence. I admit this, and therefore contend that we ought to look to future immortality, where we may obtain that fixed condition which nowhere appears on the earth" (Book III. Ch 9.5).
Prayer
The chapter on prayer is perhaps one of the most compelling parts of the book: "To know God as the sovereign disposer of all good, inviting us to present our requests, and yet not to approach or ask of him, were so far from availing us, that it were just as if one told of a treasure were to allow it to remain buried in the ground" (Book III. Ch 20.1).
In this chapter he has a section in which he does an exposition of the Lord's prayer. This part expresses a theme which runs seamlessly throughout the book beneath the surface, namely, the paternal care of God. The prayer significantly begins with the declaration that God in heaven is a Father, and "not only a Father, but the best and most merciful of all fathers, however ungrateful, rebellious, and wicked sons we may be..." (Book III. Ch 20.37).
Election
Calvin's discussion on election requires the reader to really think through their paradigms of existence. Calvin believed (along with Augustine) that God has predestined some to eternal life and some to eternal damnation:
"By predestination we mean the eternal decree of God, by which he determined with himself whatever he wished to happen with regard to every man. All are not created on equal terms, but some are preordained to eternal life, others to eternal damnation" (Book III. Ch 21.5).
He faces the obvious human objection: "... to devote to destruction whomsoever he pleases, more resembles the caprice of a tyrant than the legal sentence of judge." Calvin's response to this is to argue that this presupposes a standard of righteousness which is higher than God himself. Yet "the will of God is the supreme rule of righteousness, so that everything which he wills must be held to be righteous by the mere fact of his willing it" (Book III. Ch 23.2). In other words, the only reason we know a thing to be good or righteous in the first place is because the thing is consistent with the will of God. What would the higher standard for goodness and righteousness be? What law is it by which God must abide so that he is consistent with righteousness?
The implication of this is not a bummer. The implication is that we may trust that while these things indeed seem impossible to grasp - how he could predestine a soul to hell, and at the same time that soul willingly rejects him and resists his paternal care - but we must not fix these things with nice systems. We must presuppose that God is truly good, and he truly may elect whom he will for salvation.
If the doctrine of double predestination brings your heart to a kind of rage, you will still be able to enjoy the Institutes. The doctrine of election only makes up about 44 out of about 1000 pages (although he does allude to it throughout the book).
Calvin's Institutes offers a holistic vision of humanity through the lens of the reformation. This is a theology book. It is about ultimate reality, and it is 1000 pages of compelling argument that the meaning of all reality and every human being is the glory of God in Jesus Christ, the living Word, as witnessed by Scripture, the written Word.