(Polarity is a term from Coleridge via Barfield meaning a dyadic relationship between two distinguishable but inseparable complementary elements - it implies that fundamental reality and priority of dynamic process - of creation and procreation. The prime polarity is love of two distinct, complementary, eternally wedded persons.)
Spiritual progression is a sequence of deaths and births.
The conception then birth of Jesus was the death of Jehovah, when Jehovah (who made this earth) became a part of a polar dyad with Man; Jesus's baptism was the birth of Christ in dyadic polarity with the Holy Spirit; the resurrection of Jesus Christ required his death and a polarity with The Father.
Baptism and Marriage imply the death of a previous singleness and birth of a new dyadic polarity.
Truly to be born-again as a Christian is death of what we previously were; the birth of a child is the emergence of a new relationship of parenthood - and the death of our previous state.
An eternal marriage of a fully divine son and daughter of God is a recapitulation of the primal dyad - and the ultimate creative polarity; capable of procreation of new spirit children from primordial human 'intelligences' - as well as of 'normal' creation.
(I presume that marriage was the final stage in the theosis of Jesus Christ - by which he achieved the full nature of the Father; such is - I believe - represented in John's Gospel.)
Because what emerges is a new polarity, to be Christian it is not a static state - it is the balance of a polarity - and that balance may go in either direction, even a long way towards apostasy, without the polarity being destroyed - so long as repentance is effectual.
(The sin against the Holy Ghost refers to the destruction of this polarity; which is non-viable, and a kind of death. Polar complements cannot be separated without destruction - perhaps into mere abstraction - of both parts.)
So at Christmas we celebrate a birth - which is also a death; complementary to Easter where we celebrate the same process with the opposite emphasis.
A birth is rightly to be celebrated; and for birth, death is necessary - including that death which terminates mortality and opens to resurrection.