Why is the topic of spiritual union important for Christians?

Spiritual union with Christ underscores the foundation of a believer’s relationship with God. As articulated in Ephesians 1:4, believers are 'chosen in Him before the foundation of the world,' highlighting the eternal aspect of this union. John 15:5 reinforces this as Jesus declares, 'I am the vine, ye are the branches,' emphasizing that apart from Him, believers can do nothing. This union not only provides believers with spiritual sustenance but also instills a profound dependence on Christ. It assures that their faith and fruitfulness stem from this intimate relationship, thus making it central to their sanctification and growth in holiness.