Second Vatican Council Explained - Key Points and Insights on the Council that Updated the Catholic Church 60 Years Ago

The Second Ecumenical Council of the Vatican, commonly known as the Second Vatican Council, or Vatican II, was the 21st ecumenical council of the Roman Catholic Church. The council met in St. Peter's Basilica in Rome for four periods (or sessions), each lasting between 8 and 12 weeks, in the autumn of each of the four years 1962 to 1965. Preparation for the council took three years, from the summer of 1959 to the autumn of 1962. The council was opened on 11 October 1962 by John XXIII (pope during the preparation and the first session), and was closed on 8 December 1965 by Paul VI (pope during the last three sessions, after the death of John XXIII on 3 June 1963). 

Pope John XXIII called the council because he felt the Church needed “updating” (in Italian: aggiornamento). Sixteen magisterial documents were produced by the council that proposed significant developments in doctrine and practice.

Pope John XXIII opened Vatican II by delivering his famous 'Gaudet Mater Ecclesiae' speech, in which he indicated the main purpose of the Council.
It gathered nearly a century after Pope Pius IX convoked Vatican I (1869-70) which defined the dogmas of papal infallibility and the primacy of papal jurisdiction.
Pope John wanted a pastoral Council and one of renovation, so that the Catholic teachings could be better understood and accepted in 20th-century society. As he said at the opening speech of the Council, while preserving the integrity of its doctrine, the Church wanted to offer the modern world the "medicine of mercy", and not severe condemnations.
Between 2,000 and 2,500 Catholic cardinals, patriarchs and bishops from all over the world, assisted by 460 theological experts (periti), attended each session. For the first time Protestants, Orthodox and other non-Catholic observers were invited to assist. 42 lay and religious listeners, men and women, also attended.
16 documents
Overall, the Council issued 16 documents, including four Constitutions (on the Church's structure and nature, on divine Revelation, on the Church in the modern world, and on the liturgy,); nine Decrees (on the Church and the media, ecumenism, Eastern Catholic Churches, bishops, priestly formation, religious life, the laity, priestly ministry and missionary activity. Three Declarations (on non-Christian religions, Christian education and religious freedom were also issued.
The four Constitutions: 
‘Lumen Gentium’
One of the most important documents produced by Vatican II is the Dogmatic Constitution ‘Lumen Gentium’ on the Church's structure and nature. It presents the Church as a Mystery and a Communion of baptized believers (the “People of God”) who are called to holiness and who each have specific roles and responsibilities. It reaffirms the missionary character of the Church and confirms the collegiality of the Episcopate "with and under the successor of St. Peter".  It establishes, among other things, the  faculty for the local Episcopates to restore the permanent diaconate for  married men. The role of the laity and their participation in the life and mission of the Church is also emphasized, while the vocation to religious life is considered in relation to the spiritual life of the whole Church.
‘Dei Verbum’
The Dogmatic Constitution ‘Dei Verbum’ on Divine Revelation is another fundamental document of the Council. Its purpose is to spell out the Church’s understanding of the nature of Revelation, that is, the process whereby God communicates with human beings. It is especially relevant for ecumenism, as it touches on questions about Scripture, tradition and the teaching authority of the Church.
‘Sacrosanctum Concilium’
The Constitution ‘Sacrosanctum Concilium’ on the  Sacred Liturgy is remembered by many for having allowed vernacular languages in the liturgy, or for having emphasized the importance of community prayer recognizing  the value and richness of the various rites in the Church according to the different traditions.
‘Gaudium et Spes’
The Pastoral Constitution ‘Gaudium et Spes’ on the Church in the Modern World, called on the Church to engage in dialogue with contemporary society and its problems, bringing church teaching and moral values to bear on a world too often torn by hatred, war and injustice. The document acknowledged that science and culture have things to teach the Church, but also said the Church has a mission to sanctify the world around it.
In the years after Vatican II the Church witnessed several landmark changes:
- The new Roman Missal was issued in 1970, with a new cycle of readings designed to offer a richer selection of Scripture. The liturgical calendar was simplified. The rites for sacraments were revised, emphasizing the communal aspects of their celebration. The Rite of Christian Initiation of Adults was revived and reformed. As the changes took places, active liturgical participation increased dramatically in many local church communities.
- Lay ministries multiplied. Lay readers and lay ministers of Communion appeared during Mass. Laity were represented on parish councils and diocesan boards, and lay men and women, many with theology degrees, replaced clerics in a number of administrative church positions.
- Throughout the church, there was a renewed attention to Scriptures, in liturgy and in individual spirituality.
- Eastern Catholic churches were encouraged to return to their own traditions, ending a period of Latinization and opening a new appreciation of variety within the universal church.
- Ecumenism flourished, in formal dialogue between Catholic officials and other Christian churches, and in prayer and fellowship encounters at the local level.
- After the council acknowledged the possibility of salvation for non-Christians, dialogue also began with other religions.
- Religious life changed dramatically, as religious orders adopted Vatican norms and rewrote their own constitutions, taking a new look at issues of authority, community and identity.
- The council restored the permanent diaconate as a ministry and allowed married men to be ordained deacons. Today, there are more than 29,000 permanent deacons around the world.
- The council's teaching that the pope and bishops together form a single collegial body led to a new appreciation for bishops and bishops' conferences. The Synod of Bishops was formed to meet regularly and advise the pope.
- Theology was revitalized, especially moral theology, which focused increasingly on biblical sources and the individual conscience, and less on church law or authority.
- The council underlined the church's solidarity with humanity instead of its separation from the secular world, and this led to a mushrooming of social and charitable activities. Church leaders spoke frequently about the church's identification with the poor and suffering, and the pope became a strong human rights advocate.
Main sources:  Vatican News, CNS, Wikipedia and L’Osservatore Romano