Q. Why did the Lord say, when he was instructing the Israelites about the angel he was sending ahead of them in the wilderness, that if they didn’t obey, the angel (acting on God’s authority) would not forgive them? And why did Jesus say, after teaching his disciples the Lord’s prayer, that if we don’t forgive, the Lord in heaven will not forgive our transgressions?
I can understand why you are puzzled about these passages, because the Bible teaches generally that God’s disposition towards us is always to forgive us and restore us when we confess our sins. So why would the Bible say in a couple of places that God will not forgive us? I think there’s actually something more than meets the eye going on in both passages.
To consider the case of the angel first, there’s a verb in Hebrew that means “to lift up and take away.” It might be used, for example, in a case where someone picks something up and carries it off. However, this verb is also used just to mean “lift up,” that is, to carry or bear; or just to mean “take away.” It’s often used in that second sense to refer to forgiven sin. For example, Nathan says to David after he confesses his wrong, “The Lord has taken away your sin.” That’s the NIV translation, and it brings out the literal sense of the word. Ten other versions, however, say what it signifies, for example, the NET: “The Lord has forgiven your sin.”
Many translations also see this second sense in the passage about the angel who will go ahead of the Israelites in the wilderness. For example, the NIV reads: “Pay attention to him and listen to what he says. Do not rebel against him; he will not forgive your rebellion, since my Name is in him.” However, it seems to me that in the context, the first limited meaning, “carry or bear,” could well be intended instead. As the CEV (Contemporary English Version) puts it, “Carefully obey everything the angel says, because I am giving him complete authority, and he won’t tolerate rebellion.” So the meaning is not so much that sins won’t be forgiven, it’s that disobedience will be punished. And that’s what we see happen over and over again throughout the Israelites’ wilderness journey. Forgiveness of sin was still available through the sacrifices for sin that the law prescribed, but there were still consequences for sin. (Just as David’s sin was forgiven, but he nevertheless experienced consequences in his own life.)
As for what Jesus says, right after teaching the Lord’s Prayer, about God not forgiving us if we won’t forgive others, the rationale for this is explained well in the parable he later told about a servant who was forgiven a great debt by his own master, but who then went right out and insisted on repayment of a small debt by one of his fellow servants. When the other man couldn’t pay him, he had him thrown in prison. When the master heard about this, he brought the first servant back in and demanded, “Shouldn’t you have had mercy on your fellow servant just as I had on you?” And the master had the first servant thrown in prison.
So once again we understand the meaning from the context: The background is that we ourselves have first been forgiven all of our sins by God. In light of this, we should certainly forgive other people who wrong or offend us. But if we won’t do that, then what claim can we make on God’s mercy? We’re asking to be treated in a way we’re not prepared to treat others. And God simply says in response, “Have it your way.” So it’s not so much that we have to meet a certain condition to get God’s forgiveness, it’s that because we’ve already been forgiven, we should forgive others.
I hope these observations are helpful.