Deuteronomy opens up well enough: the Israelites are on the edge of the promised land, waiting for the word from God to go on in and take over. Their enemies will be no match for them because God is going to fight on their behalf (1:30) and the land is bursting with plenty of good things (sans Ski, BBQ and Star Wars!). However, the Israelites are afraid of what they will find when they enter the region; according to scout reports, giants are in the land (1:28). “Woe to us poor Israelite people!” They even have the audacity to think that God hates them and is so wicked as to deliver them from slavery in order to kill them.
Needless to say, God is not happy with their murmuring. His response to their bitter remarks are as follows: אם יראה איש באנשים האלה הדור הרע הזה את הארץ הטובה אשר נשבעתי לתת לאבתיכם זולתי כלב בן יפנה הוא יראנה (If a man among these men [this wicked generation] shall see the good land which I swore to give to your fathers, only Caleb, son of Jephunneh, will see it.) (1:35-36a) This clause is awkward, not containing a clear “then” to finish the “if” clause in 1:36a (unless you count זולתי as some kind of pseudo-apodosis marker, “then Caleb”). Essentially, God is stating that only Caleb will possess the land since the Israelites are not faithful enough to possess it. Naturally, one may retort “But God promised the patriarchs to give the land to their descendents, so he can’t not give it to them.” However, God is engaging in a kind of shifty promise fulfillment.
In 1:8, God tells the Israelites that he is giving the land to them on account of the promise which he made to Abraham, Isaac and Jacob, ולזרעם אחריהם (and to their seed after them). Seed in this passage is singular. However, singular verbs are often used with a collective sense (Williams, Ronald J. and John C. Beckman. Williams’ Hebrew Syntax. 3rd Ed. Toronto: University of Toronto Press, 2007, 1.) God means to give the land to the whole nation of Israel based upon the promise that he made to the patriarchs.
But because they “murmured in their tents” and accused God of acting in hatred towards them, God decides (initially) to only give the land to Caleb. Wouldn’t this be breaking his promise? Not according to the promise as stated. Since God is only obligated, according to his own promise, to give the land to a singular seed, he can give the land to only Caleb and fulfill the promise which he made to the patriarchs. Of course, God relents from narrowing his promise, although he would be entirely just to do so.
The moral of the story? God will have his way and be just every single time. Israel as a whole is allowed to enter the land on account of the sheer mercy of God, although he is within his rights to narrow the promise which he made to their forefathers.