>For example, I seem to remember that in several cases, Jesus Christ said something like: you have heard such-and-such, but now I tell you such-and-such.
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>To me, this means, among others, that humanity is progressing (or at least, is expected to progress!). For example, in the Old Testament, revenge was (more or less?) a law; Jesus teaches us that now (i.e., 2000 years ago) is the time to advance one step further, and pardon the offender.

The verses you refer to, ironically, are from the same Sermon (on the Mount) and appear shortly after Mt 5:18 that I referred to. Here, Jesus is giving deeper understanding of the law. He repeatedly says "you have heard" (as opposed to "it is written") to emphasize his opposition to the Pharisees, who were applying the laws inappropriately. And specifically, "eye for an eye" was never intended to be used to excuse personal revenge. Rather, it was to give the courts guidelines in determining proper punishment.

>I should add, lest you get a wrong impression, that I have this belief from the teachings of the Bahá'í Faith. I do not consider myself a Christian, although I do accept the Bible as Holy Scripture, and that Christ was sent by God.

I am not familiar with your faith, but your comments make me curious. If you consider the Bible to be Holy Scripture and Christ sent by God, yet do not consider yourself a Christian, then what is your understanding of Acts 4:12? It states (referring to Jesus), "Salvation is found in no one else, for there is no other name under heaven by which we must be saved."