In the Shepherd of Hermas, Similitude 9.16.1-4, we read the following:
1 Explain to me a little further,
sir, I said. What is it that you desire? he asked. Why, sir, I said, did these
stones ascend out of the pit, and be applied to the building of the tower,
after having borne these spirits?
2 They were obliged, he answered, to
ascend through water in order that they might be made alive; for, unless they
laid aside the deadness of their life, they could not in any other way enter
into the kingdom of God.
3 Accordingly, those also who fell
asleep received the seal of the Son of God. For," he continued, before a
man bears the name of the Son of God he is dead; but when he receives the seal
he lays aside his deadness, and obtains life.
4 The seal, then, is the water:
they descend into the water dead, and they arise alive. And to them,
accordingly, was this seal preached, and they made use of it that they might
enter into the kingdom of God."
Commenting on the theology of water baptism and posthumous
salvation contained in this passage Carolyn Osiek wrote that
The association of passing through
water with entering the kingdom of God (v. 2) and receiving the seal (σφραγις)
is unmistakably a reference to baptism, more explicit than the original
allusion in Vis. 3.3.5. The language of death and life is similar to Pauline
language, but is not exactly the same: here, death is the pre-baptismal state,
not the dying process that is symbolically enacted in the course of baptism.
This passage is so consciously talking about baptism that it introduces the
image of going down into the water dead in order to come up alive (v. 4), even
though there is no mention in the parable of stones descending into the water,
only being taken out. The absolute necessity of baptism is implicit here, and
these verses, without saying so, present a good argument in favor of baptism in
the name of the dead, apparently already an act of piety in first-century
Corinth. Here, though, it is actually deceased Christian preachers who
accomplish this task. (Carolyn Osiek, The Shepherd of Hermas
[Hermeneia—A Critical and Historical Commentary on the Bible; Minneapolis:
Fortress Press, 1999], 238)