Gen 12:7 The land promised

Gen 12:7   Then the LORD appeared to Abram and said, "To your offspring I will give this land." So he built there an altar to the LORD, who had appeared to him. (ESV)

Interestingly the initial promises to Abram did not mention land. He is told to go to the land that God would show him but it hasn't been explicitly promised until now. When Abram arrives in Canaan God promises it to his offspring, and later specified the duration; "forever" Gen 13:15 and the dimensions;  "from the river of Egypt to the great river, the river Euphrates" (ESV) Gen 15:18. The land is again promised as an "everlasting possession" (ESV) in Gen 17:8

While no conditions are explicitly attached to the promise there could be a hint of one in the next verse:

Gen 17:9   God said to Abraham, "As for you, you shall keep my covenant, you and your offspring after you throughout their generations." (ESV)

Later , in Deuteronomy, God makes it really clear to his offspring what will happen if they do not obey him fully:

Deut 28:58-64   "If you are not careful to do all the words of this law that are written in this book, that you may fear this glorious and awesome name, the LORD your God, then the LORD will bring on you and your offspring extraordinary afflictions, afflictions severe and lasting, and sicknesses grievous and lasting. And he will bring upon you again all the diseases of Egypt, of which you were afraid, and they shall cling to you. Every sickness also and every affliction that is not recorded in the book of this law, the LORD will bring upon you, until you are destroyed. Whereas you were as numerous as the stars of heaven, you shall be left few in number, because you did not obey the voice of the LORD your God. And as the LORD took delight in doing you good and multiplying you, so the LORD will take delight in bringing ruin upon you and destroying you. And you shall be plucked off the land that you are entering to take possession of it.

   "And the LORD will scatter you among all peoples, from one end of the earth to the other, and there you shall serve other gods of wood and stone, which neither you nor your fathers have known. (ESV)  

This explicitly says that they will be plucked off the land due to disobedience which means that God cannot have promised unconditionally that Abram's descendents will always be in the land because here he says he can kick them out. In fact, if Deuteronomy was addressed to me I would not sure whether to be joyful or fearful. It's got some scary stuff in it for those who disobey and I know what I'm like.

So, though the promises that God made to Abram did not have clear conditions attached to them, some seem to have been subsequently revealed or made clear in the law. Actually, as in much of the bible, I suspect there is more than one thing going on here. It could be that there are two promises, one conditional for natural Israel pertaining to the land and one unconditional for spiritual Israel pertaining to the new heavens and new earth. Even though the promise was forfeited by Israel's disobedience, it is fulfilled unconditionally through Jesus' obedience and through him and faith in him we inherit the whole earth. Having said that I am not sure what to make of the Jewish return to the land now. I'll look at that later.