Trinity
When it comes to the nature of God, beliefs differ significantly across the various denominations of Christianity. The most popular belief, promoted by the vast majority of churches in the world, is that God has a triune nature. This is the doctrine known as the Trinity, which defines God as one Being who exists eternally as three distinct persons — the Father, the Son and the Holy Spirit. Put simply, it is “one God in three persons”. The persons of the Trinity are not to be confused, so the Father is not the Son, the Son is not the Holy Spirit and the Holy Spirit is not the Father. All three persons of the Trinity are said to be co-equal and co-eternal, and “each is God, whole and entire.” However, each person is said to have a different role when it comes to how God relates to the world. For example, in God’s plan of salvation for mankind, the Father is said to have sent the Son, Jesus, who died on the cross for the sins of mankind. The Holy Spirit is said to sanctify believers, inspiring Christians in their day-to-day lives.
Here is a diagram that is commonly used by Trinitarians to summarise the doctrine:
A key element of the doctrine of the Trinity is the incarnation of God. This teaches that the second person of the Trinity, the Son, took on human flesh in the bodily form of Jesus. Thus, when Mary gave birth to Jesus, God entered into the creation. Jesus is said to be the God-man, who has two natures – one divine, one human. Jesus is said to be both fully God and fully man. As a result of the incarnation, humanity has been permanently incorporated into the Godhead; the Son will forever have an inseparable divine and human nature. Jesus’s humanity is not something that can be discarded or dissolved back into the Godhead. Even after his crucifixion, resurrection and ascension back to the Father, Jesus will forever exist in heaven as a glorified man, albeit God at the same time. Here is a diagram which summarises this concept: