It is about a person’s spiritual journey and progress in prayer, and intended for those pursuing a serious prayer life.
The Dark Night is NOT about the ordinary trials and ups and downs of life, even though these may ideally serve a purifying purpose.
As one progresses from vocal prayer through to meditation, after a period of time when prayer is a sweet experience of closeness to God, He then may take away all satisfaction in prayer and leave the soul in dryness, with no sense satisfaction. This is the Dark Night of the Senses, the first part of the book.
It is not the dryness that comes from slackness in prayer - on the contrary. It only happens to those who are seriously devoted to prayer and fully desirous of pleasing God. St John of the Cross gives signs as to how one might recognise the Dark Night, and how to conduct oneself in it.
Much later he talks about the Dark Night of the Spirit, which is an even more severely purifying trial in prayer and is not likely to be experienced by many. Mother Teresa of Calcutta certainly was one, and of course St John of the Cross did, and St Teresa of Avila, though she describes it differently, and St Therese of the Child Jesus towards the end of her life.
It’s not an easy read, but those who really know what he is talking about are very grateful he wrote it.
The Dark Night is about God’s action in the soul, and St John of the Cross’s Ascent of Mount Carmel kind of complements it - more about what WE have to do to detach ourselves from things of the senses, etc
Someone more qualified than me can chip in, no doubt! Hope this helps.
