Introduction
From the excerpts below, the Letter of St. James was addressed to the Christians of the Diaspora, who lived outside Palestine among the Gentiles; the First Letter of St. Peter was addressed to Christian communities living in various parts of Asia Minor. the environment there was hostile, which meant that Christians' perseverance was at risk; the Second Letter of St. Peter is addressed to Christians in general; the First letter of St. John, the fact that addresses are not mentioned suggests that it was a kind of circular letter sent to a number of Christian communities; the Second letter of St. John is addressed to a local church, very probably one in Asia Minor. the Third Letter of St. John is addressed to a Christian called Gaius, and perhaps through him to a group of Christian faithful; and finally the letter of St. Jude does not specify whom it is addressed to, but it was probably written originally for Christians converts from Judaism.
While each letter has its own content and purpose and there is very little common to them all, St. Augustine says that they were written to refute errors which were beginning to raise their head.
Below follows the excerpts in detail.
The Catholic Letters
After the thirteen letters of St.Paul and the letter to the Hebrews
come seven other letters (one by St. James, two by St. Peter, three by
St. John and one by St. Jude) which since the time of Origen, Eusebius
and St. Jerome have been known as the 'catholic' letters, letters to
the Church at large, not directed to a particular church or
individual: the second and third letters of St. John, even though they
are addressed to a private individual are regarded as appendixes to
his first letter and are also included in the 'catholic letters'
category.
Source: A GUIDE TO THE BIBLE | ANTONIO FUENTES
And also
The Catholic Letters
The canon of the books of the New Testament includes, along with the
Pauline corpus (the thirteen letters of St. Paul and the letter of
Hebrews), a group of seven others which Tradition usually calls the
"Catholic Letters" - that written by St. James, two by St. Peter,
three by St. John and one by St. Jude. Apparently the reason for
grouping them together is not because they are similar in doctrine or
style, but simply to distinguish them from the body of Pauline
letters. This grouping already existed from around the end of the
fourth century AD (cf. Eusebius of caesarea, Eccl. Hist., 3, 25,
2-3). The books have not always been given this position in the New
testament: the great Vatican and Siniatic codexes place them after the
book of the Acts of the Apostles; from the time of St. Jerome onwards,
all bibles place the immediately after the writings of St. Paul, just
before the book of Revelation. Nor were they all in the same sequence
as now: we often find St.Peter's two letters coming first; however,
from St. Jetome onwards most manuscripts place them where they
normally appear in printed bibles.
The name "catholic" was applied by Origen to the First Letter of
Peter, the first of John and that of Jude. Later Eusebius and St.
Jerome extended the title to cover all seven letters. It seems that
they were given this name because they were addressed to the whole
Church and not to particular communities or persons, as St. Paul's
letters were. By extension, the title was applied as to 1 and 2 John,
even those letters were sent to specific individuals.
Each letter has its own content and purpose and there is very little
common to them all. St. Augustine says that they were written to
refute errors which were beginning to raise their head (cf. De fide
et operibus, 14, 21). Certainly, they all evidence the teaching and
catechesis which was being given to the first communities of
Christians. For most part, using pastoral tone, they deal with
doctrinal instruction and moral teaching, all aimed at encouraging
people to live deeply Christian lives.
Source: THE NAVARRE BIBLE NEW TESTAMENT COMPACT EDITION
From the same Bible:
The Letter of St. James
Excerpt
The letter is addressed to "the twelve tribes in the dispersion"
(1:1), that is, the Christians of the Diaspora, who lived outside
Palestine among the Gentiles. Anything we know about the circumstances
in which it was written comes from the letter itself: that is, certain
defects were beginning to appear which threatened the spiritual health
of those communities. There is debate about the date of composition,
but it was probably written in the 60s AD, although some scholars
propose a later date.
The First Letter of St. Peter
Excerpt
[...] the date of composition is usually put around the year 64 or 67,
the possible years of Peter's martyrdom [...] It is addressed to
Christian communities living in various parts of Asia Minor. the
environment there was hostile, which meant that Christians'
perseverance was at risk. many of them were converts from paganism,
probably recent ones. Hence the constant reminders about Baptism [...]
As we can see from the final greeting, the letter was written in
"Babylon" (5:13), that is, Rome, the capital of the empire, as it used
to be called symbolically [...]
The main of the apostle seems to be to console Christians and exhort
them to stay true to the faith in the midst of difficulties and
persecution.
The Second Letter of St. Peter
Excerpt
[...] internal analysis makes it more difficult to attribute the
letter to Peter [...] the Tradition of the Church has associated the
Second Letter of Peter with the person of the apostle.
The letter is addressed to Christians in general, even though some
expressions imply that it was originally addressed to Christian
communities in Greece or Asia Minor. the dates of composition that
have been suggested run from year 60 to the end of the first century.
The letters of St. John
Excerpt
The First Letter of John [...] the fact that addresses are not
mentioned suggests that it was a kind of circular letter sent to a
number of Christian communities. It is likely that it was written,
after the fourth Gospel, to the Christian communities of Asia Minor
mentioned in the book of Revelation (Rev 2:1-3:22). [...]
The Second and Third Letters of St. John [...] In both letters the writer introduces himself as the "elder" (2 Jn 1; 3 Jn 1). The Second letter is addressed to the "elect lady and her children" (v. 1), a figurative way of referring to a local church, very probably on in Asia Minor. The Third Letter is addressed to a Christian called Gaius (v. 1), and perhaps through him to a group of Christian faithful. [...]
The second Letter was written as a word of warning at a time when the danger from heretics was not as great as that revealed in 1 John. the counsel the writer gives is along the same lines as that contained in the First Letter. the Third Letter, although it does not contain new teachings, is valuable testimony to the fidelity of the early Christian communities and a model of type of letters of commendation mentioned elsewhere in the New Testament [...]
The letter of St. Jude
Excerpt
[...] The letter does not specify whom it is addressed to, but it was probably written originally for Christians converts from Judaism. We do not know when it was written; maybe around the year 70.
The author seeks to exhort the faithful to put up a fight for the faith delivered to them (v. 3), reminding them that the apostles warned them in advance that ungodly people would appear on the scene, people given to licentiousness (vv. 17-18). maybe the author wrote the letter because he had learned that people like this had already wormed their way into those Christian communities (v. 4).
