It is commonly held that baptism means immersion in water. One passage that supports this view is Mark 1:9-10a (NRSV):
However, this is a simple view that does not take other passages into account. For example, in Matthew 3:11, John the Baptist says this about Jesus:
In those days Jesus came from Nazareth of Galilee and was baptized by John in the Jordan. And just as he was coming up out of the water...
So, perhaps baptism means “immersion into some medium”, since we now have examples of water, fire, and the Spirit. But even this definition doesn’t fit all of the New Testament usage.
He will baptize you with the Holy Spirit and fire.
In 1 Corinthians 10:1-2, Paul wrote:
Certainly the Israelites were not “immersed” into Moses. They passed under the cloud, not through it, and when the Israelites went through the sea it was the Egyptians who got wet.
I do not want you to be unaware, brothers and sisters, that our ancestors were all under the cloud, and all passed through the sea, and all were baptized into Moses in the cloud and in the sea...
In Luke 12:50, Jesus says:
This refers to His coming crucifixion in which He takes on the sin of the world.
I have a baptism with which to be baptized, and what stress I am under until it is completed!
So baptism has an even wider meaning than just “immersion”. The circumstances are lost in the fog of almost thirty years of time past, but I remember either my Greek professor, or a teacher who was an expert in ancient semitic languages, telling me that the Greeks would make pickles by “baptizing” cucumbers. The cucumbers were immersed in vinegar until they took on the quality of the vinegar.
Fortunately, I don’t have to rely on my memory. My concordance has this note concerning the definition of baptizo:
Whether or not you agree with his conclusion concerning the meaning of Mark 16:16, the examples from secular and NT usage show that the primary idea behind baptism is “identification/union”. A piece of cloth dipped into a dye can be said to have been baptized, since the cloth takes on the color of the dye. A piece of plastic dipped into the same dye has not been baptized, since no color change occurred.
The clearest example that shows the meaning of baptizo is a text from the Greek poet and physician Nicander, who lived about 200 B.C. It is a recipe for making pickles and is helpful because it uses both words. Nicander says that in order to make a pickle, the vegetable should first be 'dipped' (bapto) into boiling water and then 'baptised' (baptizo) in the vinegar solution. Both verbs concern the immersing of vegetables in a solution. But the first is temporary. The second, the act of baptising the vegetable, produces a permanent change.
When used in the New Testament, this word more often refers to our union and identification with Christ than to our water baptism. e.g.Mark 16:16. 'He that believes and is baptised shall be saved'. Christ is saying that mere intellectual assent is not enough. There must be a union with him, a real change, like the vegetable to the pickle!
-- Bible Study Magazine, James Montgomery Boice, May 1989.