Such a reform as the secularization of land belonging to the church was discussed at the turn of the 15th and 16th centuries. But only in the 18th century did the solution to this issue finally take shape. It was in this century that the state was able to solve the problem posed during the reign of Ivan III.
Secularization is the liquidation of large church holdings. And it was with this process that the long struggle of the Russian rulers and the church for land was completed. And the fact that this happened just in the 18th century is not accidental.
By that time, big successes had been made by commercial capitalism, and the form of rights that existed in relation to church lands prevented this. The main trend was that land is a commodity from which profit should be made. This was quite satisfied with the reform of the first half of the 18th century, which freed land ownership from sovereign dependence. Meanwhile, church grounds, due to the special nature of their use, were not alienated. The clergy could only acquire them, but have no right to alienate in any way.
Such was only the general reason for the phenomenon called "secularization of church lands." There were other reasons, let's say, of a more private nature. The fact is that all policies regarding Russian lands depended very much on noble interests. This stronghold of the monarchy was striving to expand its possessions with all its might, while the free land resources of the central part of the state were already practically exhausted. Well, few people were interested in the lands on the outskirts. The nobility judged that the secularization of church estates and peasants would create a good fund that would allow them to expand further.
The ruling persons for a very long time could not decide to violate the union that was formed from the friendship of the state and the church. Only in the second half of the 18th century did objective efforts prevail. After a series of hesitations, Peter III issued a document in 1762, which was the reason for the creation of a special College of Economy, which would manage all the church estates. At the same time, it was prescribed to remove from the management of them all persons who had clerical ranks. Peasants, who worked on church estates, were obliged, instead of their previous duties, to pay a ruble dues over the salary. So, in peasant use, there remained lands that they plowed for church patrimonies, but land that was not in their use before (mills, etc.) should be given to those who wanted to be for rent. And all the amounts received were placed at the disposal of the created College. Thus, labor was not overloaded, but all the requisitions taken by the rulers would immediately be returned to the peasants.
However, this decree was valid for a short time. Due to the exceptional situation in the state, Catherine the Great had to go to the "trick". The secularization of church lands was recognized by her as a rash measure, the decree was canceled, and the churches were returned to the land, including and peasants. The Empress reopened the home churches sealed during Peter III and began to contribute in every way to the revival of the influence of clerics on censorship, etc.
The abolished secularization of church lands provoked unrest among the monastic peasants. And the nobility was, to put it mildly, dissatisfied. As a result, Catherine the Great made a new decision: temporarily suspend the abolition of secularization and create a commission for a comprehensive study of the issue. By that time, the empress had already made sure that the clergy as a political force was very weak. After all, her orders, although they caused indignation and a great murmur among the hierarchs, but no one dared to speak openly. Thus, according to the decree of 1764, all bishop, synodal, church and monastery estates were finally transferred to the jurisdiction of the College. But instead of the selected lands, the clergy now had to rely on regular maintenance, and subsequently, during the general land survey, it received small land allotments.
It is impossible to answer unequivocally what the secularization of church lands, good or bad, brought more, but the fact that this measure was really outstanding in its century is for sure.