Glorification is, in Christian theology, the final stage of salvation: the state of the redeemed in the age to come, when mortality and the effects of sin are removed and the person is conformed fully to Christ, body included. In the Protestant ordering of salvation it is the last term of a sequence, calling, justification, sanctification, glorification, and it differs from the others in being wholly future and wholly God's act, with nothing progressive or cooperative about it.
Its pivotal text is Romans 8:29-30, where the chain runs from foreknowledge through predestination, calling and justification to glorification, with the final verb in the past tense. That grammatical feature has been much commented on and is taken by Reformed interpreters as expressing the certainty of the outcome, what is still future is spoken of as already done. Paul's fuller treatment is 1 Corinthians 15, where the resurrection body is "sown in dishonour, raised in glory", and a contrast is drawn between the body as it now is and a "spiritual body", with the transformation extended to those still alive at the end. Philippians 3:21 speaks of the body of humiliation being conformed to the body of Christ's glory.
What the doctrine chiefly commits its holders to is that the final state is embodied. Christianity inherited the resurrection of the dead from Second Temple Judaism and has consistently affirmed it against accounts, Platonist and later, in which the soul's release from the body is itself the goal. What a "spiritual body" is has never been settled: Aquinas discussed the properties of the glorified body at length, and modern theology has generally been more reticent, but the claim that there is one is credal rather than speculative.
Neighbouring doctrines qualify the picture. Eastern Christianity's theosis, and its reading of the Transfiguration light, treat glorification as beginning now rather than only at the end. Catholic teaching holds that the blessed enjoy the beatific vision before the general resurrection and are glorified in body afterwards. And in ordinary usage "glorification" also names the act of giving glory to God, a second sense the tradition connects to the first by insisting that the creature's fulfilment and God's glory are not in competition, a point made most memorably in the opening of the Westminster Shorter Catechism.