The pietist movement is to some extent controversial, and there are competing understandings about what pietism is. Sidestepping those questions, however, we can simply look at some of Spener's texts directly, and not worry about the larger constructs and disputes surrounding them.
One of his most famous books is entitled Pia Desideria, in the last third of which he makes concrete suggestions about ways to improve the church:
Thought should be given to a more extensive use of the Word of God among us. We know that by nature we have no good in us. If there is to be any good in us, it must be brought about by God. To this end the Word of God is the powerful means, since faith must be enkindled through the gospel, and the law provides the rules for good works and many wonderful impulses to attain them. The more at home the Word of God is among us, the more we shall bring about faith and its fruits.
Spener here rightly and powerfully states the case about our original sin, and God's active role in sanctifying us. Where he wrote that Scripture is "the" means by which this can be brought about, we might wish that he had written "a" means - if Word and Sacrament are the means of grace, then are they not both also a means by which God can make it so that there is something good in us? Spener also touches upon the three uses of the law, but in stating that the law "provides ... many wonderful impulses," he might have stretched the law a bit further than it can go. Is it not the Holy Spirit which provides such impulses?
It may appear that the Word of God has sufficiently free course among us inasmuch as at various places (as in this city Frankfurt am Main) there is daily or frequent preaching from the pulpit. When we reflect further on the matter, however, we shall find that with respect to this first proposal, more is needed. I do not at all disapprove of the preaching of sermons in which a Christian congregation is instructed by the reading and exposition of a certain text, for I myself do this. But I find that this is not enough. In the first place, we know that "all Scripture is inspired by God and profitable for teaching, for reproof, for correction, and for training in righteousness" (2 Timothy 3:16). Accordingly all Scripture, without exception, should be known by the congregation if we are all to receive the necessary benefit. If we put together all the passages of the Bible which in the course of many years are read to a congregation in one place, they will comprise only very small part of the Scriptures which have been given to us. The remainder is not heard by the congregation at all, or is heard only insofar as one or another verse is quoted or alluded to in sermons, without, however, offering any understanding of the entire context, which is nevertheless of the greatest importance. In the second place, the people have little opportunity to grasp the meaning of the Scripture except on the basis of those passages which may have been expounded to them, and even less do they have opportunity to become as practiced in them as edification requires. Meanwhile, although solitary reading of the Bible at home is in itself a splendid and praiseworthy thing, it does not accomplish enough for most people.
Here Spener correctly points out that the Scriptures - pericopes or otherwise - read in regular services, or in additional preaching services which were common in his day and in his town, are not enough. They are good, but there are more and different ways to come into contact with God's Word. It is worth remembering that there is a difference between, for example, devotional reading of the Bible on the one hand, and Bible study on the other. To explore the richness of God's Word, and to allow the Holy Spirit to work through that Word in our hearts, we must encounter the Word more often, and in more different ways, than worship services. In regular worship, we do not encounter all of Scripture, for some passage are not in the pericopes, and will never occur even when the preaching adds extra texts from beyond the pericopes. In worship services, too, we are not exposed the text in its context, but rather it is isolated, and we are not exposed to the text for its own sake, but rather for the purposes to which the sermon will use it.
