Evensong is a short (40-minute) service of choral music, chant, and prayer, sung by the Choristers on Sundays at 5:00 pm. 

The service at St. John the Divine also includes a short sermon.

Evensong sample from Music at St John's Victoria on Vimeo.

Evensong is based on the medieval monastic offices of the Roman church (the English Book of Common Prayer combined the multiple hours of observance for the medieval monks into two: matins and evensong), and at its simplest level marks the passing of another day.

Typically sung in the cathedrals and college of England and the Anglican Church, its texts and canticles have provided inspiration over the years for countless musical settings by the finest composers of the English tradition, from Tallis (16th-century) through Michael Finnissy (21st-century).

As most of the service is sung by the choir on behalf of those present, one can approach this service as one likes:  there is little requirement for active participation; one may follow along with the prayer of the service, or merely bask in the music and atmosphere. Alan Wilson said of Evensong in the Guardian:

Today, evensong is the most used part of the Book of Common Prayer, largely untouched by the liturgical reforms of the past 40 years. It continues to inspire and support some of our culture’s most sophisticated musical endeavours. The passions that surround its observance are implicit, but it provides a firm peg on which to hang deeply personal reflections and memories, most of them nothing to do with Christian doctrine, which linger long after [its end].

The service itself starts with a set of responses (“O Lord, open our lips; and our mouth shall show forth thy praise”) and continues through a psalm, a set of canticles (the Magnificat and the Nunc Dimittis) and two short readings, further chanted responses and prayers (including the Lord’s Prayer), a choral anthem, and concludes with a set of prayers reflecting current events or concerns. 

The prayers of intercession, the scripture readings, and the short reflection or sermon are the only parts of the service which are spoken, rather than sung.  At St John’s, there are usually also two hymns which those attending can join in singing if they desire.  The service is accompanied by St John’s impressive organ

If you enjoy this style of worship and prayer, the BBC broadcasts Choral Evensong from a different English cathedral or college each week.