The actually lectionary lesson begins at verse 23, but let's pick up Paul's argument at verse 19.
3.19: Paul literally writes: "Why then the law?" Perhaps the great question is: What does Paul mean by "nomos" or "law" here? Well...let's see!
3.19: Paul here writes that the law was added "archis" (until) "whom the one came..." Just a note here; we will come back to this later.
3:19: The NIV and NRSV/NET differ in how the translate a little relative pronoun "whom" (literally hoo or 'who') The NIV reads: "until the Seed to whom the promise referred had come" The NRSV/NET read: until the Seed would come to whom the promise had been made. I confess I am not the greatest in reading relative pronoun sentences, but I see little support for the NIV translation grammatically. The NIV basically says that a dative pronoun refers to a subject, ie, they translate whom was promised as "who was promised." I realize if you look at this too long it all looks alike, but the question is: What came? The promised seed (NIV) or the seed to the promised (NRSV/NET).
3:19: Point about how Greek works: Paul switches back to talking about the law in the latter half the sentence. How do you know? Because the aorist partiple beginning this part of the sentence is in conjugated as a masculine nominative and thus refers back to the law (alos a mas. nom). If it referred to the seed it would be neuter; if it referred to the promise it would be feminine. Participles are conjugated based on what they relate to in the main sentence; relative pronouns are conjugated based on what they relate to in the relative clause.
3:20: Paul is laying the smack down here. In Greek. In English. Anyway, moving on.
3:21: Great example of an ei-an clause. If both are in the indicative, this means that both points are wrong: If the law could give life (but it doesn't); then you could have righteousness (but it doesn't).
3:22 The NIV is hopefully creative here in its translation of "synklei-o" to mean "declares." It means "shut off" or "imprisoned" and would be used, for example, to talk about catching fish in a net. By translating this word as "declared...by the power of sin..." it distorts the Scripture to protect Scripture. The much more natural reading of the verb "synklei-o" and "hypo twn amartian" (under sin) is what the NRSV/NET render it: Scripture has not simply declared, but has actually done the deed itself. Scripture, has like a net, caught us up under sin. That's the image. Now you can figure out what that means.
3:22 See my notes last week on "Faith of Christ". Another interesting note is thatthe faith (noun) of Jesus makes possible the believing (verb; action) by us.
3:23 To further my point about the verb "synklei-o) see (3:22), the NIV translates it in this sentence as "lock-up."
3:23 Here comes another translation issue on a preposition: eis. This little bad boy can mean until or toward or to. So, the question for interpreters of Gal 3 is: Does the law lead us until Christ or up to Christ or toward Christ?
3:24 The great word here is "paidagogos" (literally foot-leader). As Liddell-Scott puts it: a boy-ward; at Athens, the slave who went with a boy from home to school and back again, a kind of tutor, Hdt., Eur., etc.:-hence Phoenix is called the paidagogos of Achilles. The law is slave...
3:25 The participle here is a genitive absolute (they stick everything in genitive to start out the sentence that has nothing to do with the second half). So you have to treat the genitive word and the genitive participle as all in the nominative and then put a coma: "Faith came," Or to make it connect: After faith came...
3:25 The Bible never says what the NIV says here: "We are no longer under the supervision of the law." It simply says, "We are no longer under a paidagogos."
3:27 Compare this verse with Col 3:12. Can you see the difference in Greek?