Transitoriness
Life is transitory, and the very opening of the play announces that it will show us "how transitory we be all day" in our lives. The play documents Everyman's journey from sinful life to sin-free, holy death - and its key theme is how we can't take things with us beyond the grave. Life is transitory - always changing, always in transition, always moving towards death. Only heaven or hell is eternal.
Sin
One way of looking at the play and Everyman's forsaking friends is by grouping them according to the seven deadly sins. It's certainly true that each sin could be found in the play, but sin itself is a wider theme in the play: Everyman has to absolve himself of sin to go to heaven.
Death
That the play is about death is foregrounded when, early in the play, a personified Death appears at God's summons. Death's role is to bring people to judgment. Though the play doesn't particularly explore our emotional response to Death, it is important to note that Everyman's pilgrimage is to the grave - and that the whole play is a consideration of what man must do before death.
Pilgrimage
A pilgrimage is a journey taken to a sacred or religious place, and it has often been noted that Everyman's journey through the play is in some sense itself a pilgrimage: a religious journey taken, ultimately, to heaven. Medieval writers often compared life to a pilgrimage: a transitory journey to an ultimately spiritual goal. Comparisons might also be made with those in holy orders, who, like Everyman, must learn to live without belongings and let go of the things they are attached to in order to progress on a spiritual journey.
Worldly Goods
Everyman is - notably - deserted by his Goods about halfway through the play, and told that love of Goods is opposite to love of God. For Everyman, who is finely dressed, and whose friend, Fellowship, holds a new robe in high esteem, part of the progression of the play is learning not to be attached to worldly goods, and to focus his attention instead on things with spiritual value.
Reckoning and judgement
Everyman has to clear his book of reckoning before he can progress to heaven, and one of the things the play considers is how humans will be judged after they have died. God is furious that humans are living a superficial life on earth, focusing on wealth and riches, without worrying about the greater judgment that is to come - and, notably, Everyman's own judgment - his ability to understand his life - becomes gradually more and more enlightened on his pilgrimage towards his heavenly reward.
Earthly versus spiritual
At the beginning of the play, God is furious that humans are concerning themselves with worldly things and not with their ultimate spiritual judgment - and whether they will dwell in heaven or hell. People are "living without dread in worldly prosperity". The play constantly explores the conflict between worldly concerns, riches, clothes and relationships, and the need to focus on spiritual welfare, heaven and hell and God's judgment.
