What is happening here
On Sundays and major feasts, the Liturgy of the Word includes a Second Reading taken from the New Testament — usually one of Paul's letters, occasionally the Letter to the Hebrews, the Catholic Epistles (James, 1 and 2 Peter, 1, 2, 3 John, Jude), or the Book of Revelation. The Second Reading expands the Liturgy of the Word beyond the First Reading's usually Old Testament voice and the Gospel's Christ-centered narrative, giving the assembly a third witness to the Word of God.
On weekdays, the Second Reading is omitted; the structure goes First Reading, Psalm, Gospel. On Sundays, however, the three-fold Liturgy of the Word — Old Testament, Apostle, Gospel — is the standard pattern. The thematic relationship between the readings varies: in Ordinary Time, the Second Reading is on its own track (working semi-continuously through Paul and others), while in special seasons (Advent, Lent, Easter) all three readings often share a common theme.
For Catholic weddings, the Second Reading is a particularly important choice. The lectionary offers a curated set of New Testament passages on Christian love and marriage — 1 Corinthians 13 ("Love is patient"), Ephesians 5 ("This is a great mystery"), 1 John 4 ("God is love"), and others. The choice often shapes the homily and the theological tone of the entire Mass.
For Catholic funerals, the Second Reading typically comes from Paul's writings on resurrection (Romans 8, 1 Corinthians 15) or from the Book of Revelation (the new heaven and new earth). The choice anchors the funeral in the explicit Christian hope that death has been defeated.