From the moment Russia was baptized into Christianity by Saint Vladimir in 988 to the 17th century rule of Tsar Aleksei Mikhailovich, the Orthodox Church was the organic core of the Russian civilization. In the words of Alexander Solzhenitsyn:
In its past, Russia did know a time when the social ideal was not fame, or riches, or material success, but a pious way of life. Russia was then steeped in an Orthodox Christianity which remained true to the Church of the first centuries. The Orthodoxy of that time knew how to safeguard its people under the yoke of a foreign occupation that lasted more than two centuries, while at the same time fending off iniquitous blows from the swords of Western crusaders. During those centuries the Orthodox faith in our country became part of the very pattern of thought and the personality of our people, the forms of daily life, the work calendar, the priorities in every undertaking, the organization of the week and of the year. Faith was the shaping and unifying force of the nation.The 17th century, however, saw an abrupt and violent change to this state of affairs. Again, in the words of Solzhenitsyn:
But in the 17th century Russian Orthodoxy was gravely weakened by an internal schism. In the 18th, the country was shaken by Peter's forcibly imposed transformations, which favored the economy, the state, and the military at the expense of the religious spirit and national life. And along with this lopsided Petrine enlightenment, Russia felt the first whiff of secularism; its subtle poisons permeated the educated classes in the course of the 19th century and opened the path to Marxism. By the time of the Revolution, faith had virtually disappeared in Russian educated circles; and amongst the uneducated, its health was threatened.By the time Tsar Nicholas II inherited the throne in 1896 the Russian society was suffering from a deep spiritual crisis: most of the ruling class was highly secularized if not completely materialistic, almost every single aristocratic family had joined the Freemasonry, while the rest of the country, still mostly composed of peasants, was nominally Christian Orthodox, but not in the deep way the Russian nation had been before the 17th century.
Russian Tsars often ended up being real persecutors of the Russian Orthodox Church, in particular those upon whom the Russian aristocracy and the West bestowed the title of "Great". Peter I, the so-called "Great" decapitated the Russian Orthodox Church by abolishing the title of Patriarch from the head of the Church and replacing him by "Synod" run by a laymen bureaucrat with the rank of "Chief Procurator" who did not even have to be Orthodox himself. De-facto and de-jure in 1700 the Russian Orthodox Church became a state institution, like a ministry. Under Catherine I, also called the "Great", monastic were persecuted with such viciousness that it was actually illegal for them to possess even a single sheet of paper in their monastic cell, lest they write something against the regime.
Other Tsars (such as Alexander II, or Alexander III) were far more respectful of the Church and Tsar Nicholas II, who was a deeply religious and pious man, even restored the autonomy of the Church by allowing it to elect a new Patriarch.
And yet, by and large, the Russian Orthodox Church underwent a process of quasi-continuous weakening under the combined effects of overt persecutions and more subtle secularization from the 17th to the 20th century.
In the 20th century during the reign of Tsar Nicholas II, Russian Orthodoxy saw a short but amazing rebirth immediately followed by a mass persecution under the Bolshevik rule whose viciousness and scale was previously unheard of in the history of the Church. Again, in the worlds of Solzhenitsyn:
The world had never before known a godlessness as organized, militarized, and tenaciously malevolent as that practiced by Marxism. Within the philosophical system of Marx and Lenin, and at the heart of their psychology, hatred of God is the principal driving force, more fundamental than all their political and economic pretensions. Militant atheism is not merely incidental or marginal to Communist policy; it is not a side effect, but the central pivot. The 1920’s in the USSR witnessed an uninterrupted procession of victims and martyrs amongst the Orthodox clergy. Two metropolitans were shot, one of whom, Veniamin of Petrograd, had been elected by the popular vote of his diocese. Patriarch Tikhon himself passed through the hands of the Cheka-GPU and then died under suspicious circumstances. Scores of archbishops and bishops perished. Tens of thousands of priests, monks, and nuns, pressured by the Chekists to renounce the Word of God, were tortured, shot in cellars, sent to camps, exiled to the desolate tundra of the far North, or turned out into the streets in their old age without food or shelter. All these Christian martyrs went unswervingly to their deaths for the faith; instances of apostasy were few and far between. For tens of millions of laymen access to the Church was blocked, and they were forbidden to bring up their children in the Faith: religious parents were wrenched from their children and thrown into prison, while the children were turned from the faith by threats and lies...