Source: Devorah Dimant, "Qumran Sectarian Literature," Jewish Writings of the Second Temple Period, ed. Michael E. Stone (Philadelphia: Fortress, 1984) 499.
"In this respect the sect resembles the Pharisaic Haburoth...but unlike the latter it connected the maintenance of purity with the idea of repentance. True purity of the body became effective only when repentance takes place, i.e. by accepting the sectarian way of life. In this context, ritual purity is seen as only one facet of a more comprehensive idea of purity: purity from sin."
Dimant is talking about the entrance requirements of the Qumran sect, as they're outlined in the Community Rule.
This quote reminds me of what Josephus says about John the Baptist in Antiquities 18:117 (in whatever translation BibleWorks is using):
"[F]or Herod slew [John], who was a good man, and commanded the Jews to exercise virtue, both as to righteousness toward one another, and piety toward God, and so to come to baptism; for that the washing [with water] would be acceptable to him, if they made use of it, not in order to the putting away [or the remission] of some sins [only], but for the purification of the body: supposing still that the soul was thoroughly purified beforehand by righteousness."
Josephus' statement about John's baptism has long puzzled me. According to Josephus, John's baptism was about bodily cleansing. It wasn't really about purification of the soul from sin, since people accomplished that through repentance and righteousness. Rather, in the same way that people in the Hebrew Bible bathed after touching a corpse or having an emission of semen, John washed Jews' bodies through baptism. There really wasn't anything spiritual about it! As far as Josephus is concerned, it was a matter of ritual purity, presumably designed to maintain God's presence in Israel.
That's not really what I find in the Gospels. There, John's baptism is associated with repentance and the forgiveness of sins (Mark 1:4; Luke 3:3). For the Gospel writers, baptism was about more than giving the body a ritual bath, for it had a spiritual significance.
Another verse that touches on bath vs. spiritual cleansing in baptism is I Peter 3:21: "And baptism, which this prefigured, now saves you--not as a removal of dirt from the body, but as an appeal to God for a good conscience, through the resurrection of Jesus Christ" (NRSV).
Some Christians claim that Peter is not talking here about water baptism. In their eyes, he's saying: "The baptism that saves you is not the one where you get wet and clean dirt off your body. Rather, it's having a good conscience--becoming spiritually clean."
Others say that Peter is talking about water baptism, saying something like: "Water baptism saves you, but not because it gets dirt off your body. Rather, it saves you by making you a new man--one who's dead to sin and alive to God in Christ Jesus." Proponents of this view probably have in mind passages like Romans 6.
Interestingly, Paul talks about bodily purification. In II Corinthians 7:1, he states: "Since we have these promises, beloved, let us cleanse ourselves from every defilement of body and of spirit, making holiness perfect in the fear of God." But I don't think he's talking about taking a physical bath. Rather, he means fleeing sexual immorality, since he says in I Corinthians 6:13-20 that it is sin against the body. In my opinion, Paul equates bodily defilement with sexual immorality, since it is the body that commits those types of sins. I got this insight while I was reading early Christian literature, though I'm not exactly sure where I found it.
I guess that the Qumran community had a combination of the two perspectives. It embraced ritual purity in that it had physical baths. But it managed to incorporate spiritual purity into ritual purity. Maybe John the Baptist did the same thing, for he baptized people with water, and yet the Gospels claim that his baptism had spiritual significance.