Regarding the concept of the believers' union with Christ, much attention has been paid to the theology of the Pauline letters. C. Campbell (2012) for instance shows that union with Christ is crucial for Paul. New Testament scholars have only recently delved into the Johannine concept of union with Christ. This is remarkable, while 'the Johannine literature contains some of the richest participatory language found in the New Testament' (Macaskill: 2013, 251). This recent research into Johannine texts has brought important nuances to the fore, such as the relationship in the Fourth Gospel between the motif of the oneness of Father, Son, and Spirit and the participation of the believers in the Son through the Spirit. Macaskill already exhibited that 'the participation of believers in the communion of the triune God proceeds from this primary union [between Father and Son through the Spirit]' (Macaskill: 2013, 270). A. Byers (2017) noted that this relationship between divine oneness and the believers' union with Christ does not entail the full deification of believers. He uses the concept of theosis to argue that believers are taken into communion with God, but they are not included in the divine identity that is shared between Father, Son, and Spirit. This paper will explore, in line with Macaskill and Byers, the relationship between divine oneness and the communion of the believers with God in John's Gospel. I will argue that the communal identity between Father, Son, and Spirit is presented by John as a closed relationship between the divine Persons which is communicated to the believers and the world. Yet, the believers have communion with the Son and the Father through the Spirit by filiation 'from above' (Joh. 3,3). John is perhaps more pronounced than Paul in linking and distinguishing the oneness of the divine Being and the union of the believers with the triune God, thus providing another (biblical) perspective on the theological theme of union with Christ.