There are a lot of issues brought up in chapter 12, but since I think I've covered a great number of them in previous posts, I may be able to get through a great deal of this if not all. Also, for those of you keeping score at home, read carefully because I'm going to admit that I think there is something legitimately wrong with this chapter; how important the problem is up to the individual reader to decide.
The first few issues of this chapter are ones that I either covered in the last post or in the comments attached thereto. What is the point of all this blood being smeared on doorposts? Well, I think the central place to find this answer is in verse 13, where God claims He will spare the houses that have the blood on them. This is part of the ongoing theme of God overlooking the sins of those who cover their sin with a sacrifice. In this case, it's a national sin of Egypt, both that they held the Israelites as slaves, but more importantly that they killed all the Israelite baby boys several years back. I'm guessing the fact that this is a national sin is the reason why this plague, unlike many of the previous ones, is a potential threat to everyone in Egypt, even the Israelites. It may be that all the Israelites put the blood on their doors, and none of the Egyptians did, but I tend to think that there may have been exceptions on both sides, the results being dead Israelites and living Egyptians, since God says His criteria will be the blood mark.
Now sticking to this issue and jumping down further in the chapter, to verses 29 and 30, this is where I have an issue. I will admit that Christians actually are surely the most guilty of overassuming this sort of thing, but I think that sometimes when the Bible says "all", it's not being as precise as it ought to be, and this is illustrated twice in these two verses. Firstly, the cattle are killed. The SAB points out that the cattle were already "all" killed twice in chapter 9. I addressed it a bit there, but it's evident that only cattle left outside were harmed in the first two plagues that killed cattle. I would think that it's safe to assume (if one accepts the assumptions that I have already made about firstborn humans) that any cattle inside a house with blood on its doorposts would survive the night.
And so the verse that I have issue with here is verse 30, which claims "...there was not a house where there was not one dead." This is clearly not true in the broadest sense, as of course there were numerous Israelite houses with nobody dying. On top of that, there are some important issues demographically. Skeptics often read this verse and say, "There goes God killing a bunch of defenseless babies..." In fact, while surely many babies were killed on this night, I believe among those killed, a minority were infants. Ah, I'm mingling two issues here, but they are interrelated. Let's give some hypotheticals. Imagine an Egyptian house in which there is a man and a woman with no children, and the husband is not the firstborn of his family; result: no deaths. Imagine a house in which there are many children, but what with infant mortality being a reality, the firstborn son has already died years ago; result: no deaths. What if they have only daughters? No deaths. What if the firstborn has grown up and already moved out? No deaths. That adult child may die in his own house, or it may be that only children were affected, I don't think we know for sure, but if only children are effected, it may be that any children over a certain age (perhaps 13?) were spared. Lastly, in response to the claim of killing babies, I would venture that a very small portion of the houses with a dying child lost an infant. After all, if you have more than one child, the firstborn is probably at least a year old. Not that killing toddlers is so much better, but I figure you might as well be clear. In summary, blood or no blood, I think many houses were spared, and among those not spared, most lost an older child.
So, back up to verse 13, the SAB asks "How many gods are there?" While I addressed some of the issues raised on that page previously, I didn't address them all, as that page is actually quoting numerous passages that have multiple ways to understand them. The majority of them fall under the same classification as this verse, that is, verses that explicitly refer to other gods. The answer is, of course, that there is only one God. So why all the stuff in the other column? There are at least three approaches, and any or all of them can be suitable.
First, the literary approach, for lack of a better name. What do Hercule Poirot, Sherlock Holmes, Jessica Fletcher, and Batman have in common? They're all detectives. Does the fact that they are also all fictional characters make them any less so? Zeus, Odin, Osiris, Quetzalcoatl, Vishnu and Buluku? They're all gods, whether or not there is an actual existing entity behind each name.
Secondly, the sociological approach. Some say that a "god" is anything you give reverence to, whether it is a supposedly intelligent supernatural entity or an abstract concept. If the most important thing in your life is being rich, then money is your "god". If the most important thing is getting laid, then sex is your "god". If you want to serve Ganesh, then Ganesh is your god, whether or not Ganesh actually exists.
Thirdly, there is the spiritual approach. Suppose you decide that the world was not created by the God of the Bible, but by a superpowerful being named "Asdfgh". Maybe you made up Asdfgh, or maybe someone told you about Asdfgh and you believed. You're going to devote your life to worshipping Asdfgh out of great reverence for him/her and his/her creative and sustaining power. Who's to say that Asdfgh is not a real being, despite the fact that what you believe about Asdfgh is completely false? Generally, this goes somewhat hand-in-hand with the second approach, but with the added fact that the thing worshipped is real, albeit deceptively so. Perhaps Asdfgh was a fallen angel who told some humans he/she deserved worship. Maybe somebody dreamed Asdfgh up, and a being, wanting to lay claim to the worship Asdfgh was receiving, stepped in to claim it. Spiritually, anything could conceivably be possible. The implications of this are huge, though, and somebody may bring up some of them in comments, who knows?
In verse 14, an important question is raised, which I am going to give as short an answer as I can, since my last one was probably way too long. "Must Christians obey Old Testament laws?" Once again, the answer is "Yes and no." In all of those passages quoted, I would say that the "you" referred to is the nation of Israel. Despite the fact that Jesus came and fulfilled the law (as they say, that's an odd claim for numerous reasons), there is much of it that remains in effect for Jews. Gentiles are not required to become Jews to follow Jesus. However, there are some rules that God wants everyone to follow, and admittedly, it's not always 100% clear to me where the dividing line is.
How many days is unleavened bread to be eaten during Passover? That's an easy one. Seven days. The passage in Dt.16:8 says "Six days thou shalt eat unleavened bread: and on the seventh day shall be a solemn assembly to the LORD thy God: thou shalt do no work therein." I see no reason to assume this passage is saying that the seventh day is a day to eat leavened bread, especially since it follows so close on the heels of verse 3. I may have mentioned it before, but if two passages seem to contradict each other and are right next to each other in the Bible, you're probably misreading them. (Here's one of the best examples.)
I have already addressed the issues of stealing, population explosions, length of the captivity, and slavery, so all that remains is the objection on verse 43 and following. I don't understand it, though. Okay, so a foreigner (et al) cannot eat of the Passover, so what? It's a Jewish religious observance, and I would assume that if a person really wanted to partake of it, then they would convert to Judaism, get circumcised, and then there would be no problem, would there?