In the Catholic Church's calendar, the seasons of Advent, Christmas, Lent and Easter all have easily identifiable themes connected to the life of Christ. The season known as "Ordinary Time," on the other hand, is often thought to be a "general" season with no particular focus.
In reality, Ordinary Time has a primary focus on the years of ministry of Jesus Christ and the need for growth and maturation in the life of the Christian. This is one reason why green was chosen for this season, symbolizing the need for growth.
Connected to this spiritual theme is the "universal call to holiness," and a particular focus during Ordinary Time on the celebration of saints' feast days. In between Sundays the Church often celebrates the lives of saints at daily Mass and in the Liturgy of the Hours. Instead of wearing green at Mass, the priest may wear red or white depending on the saint's manner of death.
Historically this focus on saints was even more evident. For example, this season in the Church's calendar was divided up into "mini-seasons" based on certain feast days. The St. Andrew Daily Missal explains this particular development.
[The] feasts of saints occupy an important place during the Time after Pentecost ... Formerly it was still more noticeable; the Sundays of this season were, practically speaking, inserted between the feasts of saints and they were counted ... in relation to the feasts of SS. Peter and Paul, St. Laurence, St. Michael, who in this way dominated the whole of this part of the year.
Instead of celebrating the "Twelfth Week in Ordinary Time," Catholics would celebrate the "First Week after the Feast of the Apostles." With this in mind Ordinary Time can easily be called the "season of saints," where the Church highlights the lives of particular saints who stand out for us as exemplary examples of holiness.
It should remind us that we too are called to be saints, no matter what profession or state in life we find ourselves in. All are called to become saints, even though most of us will never be officially recognized as saints after our deaths.
The key during this season of the Church's calendar is to grow in our life of faith and attach ourselves more firmly to the body of Christ, allowing the holiness of Jesus to permeate every aspect of our lives. The saints show us the way, and it is up to us to follow in their footsteps.