The Assumption of Mary and 1 Timothy 6:16?
He alone is immortal and dwells in unapproachable light. No one has seen him or is able to do so. To him be honor and everlasting power. Amen. - 1 Timothy 6:16 (New Catholic Bible)
Will try to answer your question from a Catholic perspective, although other denominations such as Orthodoxy will be somewhat close to this same perspective.
To start off with, Catholics believe that every human being has an immortal soul and on the last day the Day of Judgement, our bodies and souls will be united. Those who are holy will be united in heaven and those who are evil will be united with their physical bodies in hell! I know this is simplifying the doctrine, but that is what the Church teaches.
As a Catholic, we believe that the soul of very holy individuals go straight to heaven waiting to be united to their physical bodies!
When if comes to the Blessed Virgin Mary, we believe the Mary was assumed body and soul into heaven as a divine privilege from Almighty God as Mary was preserved from all stain of original sin and and as such she was exempt from the curse levied against Adam and Eve, our first parents. This prerogative and the belief that the Church believes the Mary never sinned makes the Assumption of Mary a doctrine held by Catholics.
We declare, pronounce, and define that the doctrine which holds that the most Blessed Virgin Mary, in the first instance of her conception, by a singular grace and privilege granted by Almighty God, in view of the merits of Jesus Christ, the Saviour of the human race, was preserved free from all stain of original sin, is a doctrine revealed by God and therefore to be believed firmly and constantly by all the faithful. - Pope BI. Pius IX Ineffabilis Deus 1854
Without the Immaculate Conception of Mary first the doctrine of Mary’s Assumption into Heaven would be harder to explain.
We pronounce, declare, and define it to be a divinely revealed dogma: that the Immaculate Mother of God, the ever-Virgin Mary, having completed the course of her earthly life, was assumed body and soul into heavenly glory.
— Pope Pius XII, Munificentissimus Deus, 1950