In the format of the Liturgy of the Hours the Office of Readings is a unique Hour that stands alone among the others. It is the only Hour which does not have a traditional fixed time associated with it and among all of the Hours it is the youngest although it replaced the oldest Hour in the former Roman Breviary in 1970. You’ll often hear people say that the Office of Readings replaced what was formerly known as Matins, but in many respects this is a whole new Hour that wasn’t merely a reform but a complete change. However, there are vestiges of the traditional form of Matins as a Vigil that remain within the rubrics around this Hour.
The fact that the Hour is not linked to a particular time of day makes is unique in many ways. In the English four-volume Liturgy of the Hours books approved for use in North America, the Hour starts with the antiphon for the Invitatory but this is purely optional and dependant on whether the Office of Readings is the first Office being recited for the day. It can be said alone as its own Office or it can be attached to another office such as Morning Prayer or even Evening Prayer if that is how you wish to pray the Hours for that particular day. Matins was always the first Hour of the day (and was usually said at night or very, very early in the morning before dawn) and thus always included the invitatory. This is not the case with the Office of Readings.
The Office of Readings is made up of three psalms or three parts of a large psalm and two readings of notable length; the first reading being from Scripture and the second from a selection of the Holy Fathers usually related to the season, feast or memorial. This is another marked departure from Matins which at its peak had over 12 psalms which formed nocturns that included up to three readings each. The readings in Matins were shorter in sections but together formed sections of Scripture and patristic readings that are comparable to what we get today with the Office of Readings.
On Sundays and solemnities one can add a vigil part to the Office that include three canticles and a reading from the Gospel (usually from an alternate year of the Lectionary from that of the current Mass). This retains the ancient understanding of the word vigil as the prayers and preparations before Holy Mass on Sunday evening after sundown on Saturday night. The Te Deum is also recited on these days just prior to the collect for the day.
There is no doubt that the Office of Readings remains controversial among Catholics. Significant changes were made to the liturgy and thus also to the Roman Breviary and Divine Office in the wake of Vatican II. Among those changes was the introduction of the Liturgy of the Hours, which brought us this new and wonderful devotion in the Office of Readings. There are people who take issue with the Liturgy of the Hours because of the many options, the four-week psalter, the omission of controversial psalms and the creation of a new Hour in the Office of Readings. But when understood in light of the overall intention of the Church Fathers during Vatican II to truly make the Divine Office accessible and palatable to lay people as well as clergy it all actually makes a lot of sense.
I’ve prayed a one-week psalter before and it is certainly wonderful and rich and but only if you have the time. Not many people have an hour in the morning to read 12 psalms (plus another five if they decide to do Matins and Lauds together which is the norm). This routine quickly goes from being wonderful and rich to being a burden and terrible. The four-week psalter is made for lay people, so that we can have access to all 150 of the psalms (the accepted ones, at any rate) but at a pace that works for ordinary life. The same goes for the creation of hinge Hours in Morning/Evening Prayer which follow a pattern typical of how laity live in the 5 day work week and eight hour work day. Remember that how the Roman Breviary of the past was developed was at a time when we didn’t use any unnatural light after sundown, people usually slept in two four or five hour periods and woke in the middle of the night to work and sometimes eat (and in the case of monks, pray). This is simply not the reality for lay people today, for anyone really, and so the changes make sense within this light.
The Office of Readings has become a key within my own prayer life. We are all called to read Holy Scripture often and we could all use more exposure to the insight of the church fathers. Having an Office that is devoted to reading the Bible and the church fathers gives me a vector to do this task which is part of my commitment to pray the Hours regularly. I find they enrich my life from a liturgical perspective and keep my mind focused on God and on the particular season or celebration of the church. There are some days when I can only complete one Hour and I am not ashamed to say that I choose the Office of Readings over all of them (usually with a confession added at the start for good measure). It really is the best of both worlds when you can pray the psalms and do some readings relevant to the season of the church or particular celebration.