We might consider two reasons for our liturgical year’s providing separate feasts for the apostles rather than a single feast to celebrate their memory. First, many of the apostles are associated with a ministry to a particular place — for example, James (the Greater) to Spain, Thomas to India, Jude to Syria and Persia. At some point the Church embraced the local traditions and invited all Catholics to participate in celebrations to honor the individual apostles.
Second, the Church tends to expand, rather than diminish, opportunities for liturgical celebration. Thus, we acknowledge groups, such as the North American Martyrs (Oct. 19), who worked and died together, and Sts. Peter and Paul (June 29), who share an undeniable link in building up the early Church. However, allowing us to celebrate feasts dedicated to the individual apostles enables us to reflect on their distinctive, personal merits, and to discern ways in which we might incorporate an apostle’s strengths (or build on his weaknesses) as we strive to live out our own apostolic witness.
Because the first Eucharistic prayer names each of the apostles, we have an opportunity to celebrate a feast in their collective honor whenever the celebrant uses that prayer at Mass.