Actually, Biblical condemnation of masturbation is rather sparse, to say the least. The most often referenced passages concern one Onan, who is commanded (directly and personally) by God to impregnate a certain woman, and instead "spills his seed on the ground" to avoid obeying the command. It's pretty clear that Onan's sin (for which God kills him) isn't masturbation per se, but violation of, as it were, a direct order. Also, in context (Exodus 38:9), Onan's seed-spilling isn't even masturbation at all; it's
coitus interruptus.
The "sinfulness" of "self abuse" falls more into the category of dogma or church doctrine, something originally decided on by Popes on vague general moral and theological principles rather than any specific Biblical text, and later retained by some Protestant sects. (In the same category is the desirability of priestly celibacy, which was considered a terrible heresy by the earliest Christian historians. The Protestants were a bit more eager to get rid of that one... can't imagine why

.)
As for the Commandment regarding working on the Sabbath, I find that an interesting and revealing example about the nature of Scripture as I see it. From a humanistic point of view, the Eighth Commandment is one of the single most effective Bible passages at improving the quality of human life over the past twenty centuries. In recent years we see it as a relatively minor issue of weighing piety versus convenience; of separation of church and state (blue laws); of balancing the respective rights of employers, coworkers, and Sabbath-observing employees. But in centuries past it meant a lot more than that. When most of the population were slaves, serfs, peasants, laborers, sweatshop workers, the absolute requirement not to work on the Sabbath often gave them their only regular respite in a life of grueling toil. Sure, it wasn't 100% reliable or equitably applied (who cooks the Sunday supper?), and the Sabbath observances themselves often involved discomfort and tedium, but it was better than "on the seventh day, we go back into the mine and dig some more."
Would this have happened if observing the Sabbath were instead written as the "Eighth Just-A-Suggestion"?
What if the Commandments aren't really about how-not-to-sin after all (though they had to be stated that way, to have been effective), but about how to build a moral civilization starting from the stone age? What if we look at other Biblical ideas, from the Old and New Testaments alike, in a similar light?
Interpreted as a guide for what is fundamentally morally right, Paul's repeated advice to slaves to serve their masters well is clearly a non-starter. But what should that advice have been? Suppose those passages instead had read, "Slavery is an abomination. Those who hold slaves must set them free; slaves that are not set free should rise up and escape or overthrow their masters, even as Moses brought the Isrealites out of bondage in Egypt." What would the effect have been, in, say, AD 300? Would it have done the slaves any good, to rise up and be slaughtered even more often than they'd already been rising up and being slaughtered since time immemorial? Would it have done Christianity any good, for every slave-holding state, city, and household to have a really good reason to eliminate, at all costs, any slave, or any person coming into contact with slaves, suspected of holding Christian views?
Even assuming the Bible is the Word of God, does God owe humanity the truth, let alone the whole truth? Where, in the Bible, does God promise to tell humanity the whole truth? Could humanity comprehend the whole truth? Could we put into effect the same knowledge of the truth in any given century? Do we tell our own young children the whole truth about everything? Now, suppose the Bible is not the direct Word of God, but the understanding of men uncommonly wise for their time, with a perception (divinely aided or otherwise) of creation that revealed to them some of the path to building more just worlds. How much of it could they, in their own world that knew only kings and subjects, masters and slaves, understand? How much of it could they put into words? Surely less than the whole truth. In that case the Bible would be a map, but the map is not the territory, and the territory ahead is always unexplored.
Did Adam and Eve really gain
all knowledge of good and evil at the moment they ate of the fruit of the tree of knowledge? Does this make sense, either literally or allegorically? Or allegorically, did that choice, that
knowledge was what they wanted, represent the beginning of the journey that we're still on today? (God: "Okay, you want knowledge. Happy to oblige. Step 1: get out of Eden.")
What, then, about sin? Some Biblical sins are, I believe, no longer sins, and some never were in the first place. Some people cling to some sins, like premarital sex, homosexuality, masturbation, and honoring the Sabbath, as if they were precious jewels, a dwindling supply that we must hoard and treasure. But the opposite is true: our increasing application of Jesus's humanistic teachings give us more sins now than ever before. Slavery, child sex, misogyny, racism, and submission (unnecessarily ceding one's human rights) are now sins; forms of "gluttony" now include environmental waste and over-fecundity; forms of "wrath" now include sectarian violence and intolerance; and so forth. Few of these sins are explicitly grounded in Scripture and some of them go against specific passages, but we draw them out of the core general principles much like the ancient Popes found the sins of masturbation and marriage of priests. Do we need a new set of Commandments ("Thou shalt not buy way too much crap thou doesn't need") or can we continute to take it from here?
I'm not sure sin and salvation are quite as important as most churches insist -- the concept of original sin itself rests on suprisingly shaky Biblical ground, and without original sin, salvation takes on a different (but if anything, more coherent and deeper) meaning. Perhaps instead of asking "is this or that, or should this or that be, a sin," one might focus on, "what should I be doing better to make the world a better place?" You know the answer. At least one, probably several, things came into your mind when you read that question.
"Go, then, and sin no more."
Respectfully,
Myriad