The Mysteries RSC, Stratford; Unicorn, London

Katie Mitchell's beautiful production of The Mysteries ends with the last occasion on which the apostles meet and share a meal with the risen Christ. Before leaving, Paul Hilton's superlative Jesus kisses each of them full on the mouth and, as he walks away, says: "Follow me". Both poignantly and stirringly, Mitchell's staging shows how the meaning of that injunction has now shifted and deepened. Instead of trooping off after Christ, as they have done before, the silent apostles gradually get up and, each shouldering responsibility for spreading the word, strike out in different directions.

It's significant that this version of The Mysteries should climax on earth with a pensive and inaugurative moment for mankind rather than down in hell with the fulfilment of God's forethought on Judgement Day. Made up from bits of all the medieval cycles and from scripture, Edward Kemp's two-play script - The Creation and The Passion - arranges and inflects the various stories so as to replace the heaven / hell scenario of the original with the theme of a return to paradise through human beings taking responsibility for themselves. You'll wait in vain, here, for the fall of Lucifer or for a smug chairman's report from God at the close of business.

Kemp is a man prepared to characterize even the Gospels as "fraught with ideologically unsavoury baggage" and some of his introductory remarks make you fear that political correctness will lie like a pall over the proceedings. In fact, staged with a lovely, elemental spareness and charged simplicity, and performed by a manifestly dedicated company, the two productions move, engross and delight throughout.

Happily, the devisors haven't dropped the idea of a deity. But from the moment when, in pitch darkness, we hear a groan turn into a chuckle and then into the whisperingly repeated, nursery rhyme-like chant of "let there be light", you get the sense that David Ryall's God - a rum old party, like some benignly bemused ex-member of the Crazy Gang - is making things up as he goes along. After the fall, he offers mankind the hope of re-entering paradise in promising them the Oil of Mercy. Thanks to the inclusion here of the not-so-well-known story of Seth (the son of Adam who travels to the gates of Eden to quiz the Angel of Justice), a recurring and growing symbol of that hope, hung with ever more petitions, is the tree that sprouts and is replanted from the seeds Seth is instructed to place in the mouth of his dead father.

A more familiar take on The Mysteries can be seen now in Richard Williams' likeable production for children at the Unicorn. Driven forward by fetchingly sung and harmonised spirituals and gospel numbers, the show appealed very much to my nine-year-old assistant but was an odd experience for me, coming to it the day after seeing the Mitchell. Take the treatment of Judas. If somebody had to betray Jesus, wasn't Judas in a way doing him a favour, my daughter wondered, after seeing him presented as the conventional malcontent in the Williams. She should have come to the Mitchell for there, so loth are they to demonise anyone, Jesus treats Declan Conlon's pained, dignified Judas as almost a loving co-conspirator, returning with fervour the kiss of betrayal.

Given to standing on his head when alone, Paul Hilton's Christ is a wonderful mix of a boyishness not yet outgrown and a precocious, piercingly paternal solicitude for his followers. His is the first Jesus I've ever heard making "yum, yum" noises before symbolic meals and the first whose love for mankind has seemed so winningly unmetaphysical.

RSC, The Other Place (01789 295623); the Unicorn, to 13 April (0171-836 3334)