Inner-biblical exegesis is trendy now in biblical studies. By searching for similar vocabulary, themes, and style, it is sometimes possible to determine that a certain writer was using and interpreting another biblical book as a source.
I have doubts, however, about our ability to detect textual borrowing, and many of those who draw parallels between biblical texts seem to be grasping at straws sometimes. Even if textual borrowing is detected, it is then virtually impossible to detect the direction of literary dependence without following a priori assumptions about the relative dating of biblical books.
For example, Second Isaiah likes to use the image of the ecological transformation of the desert into a fertile oasis accompanying Israel's return from exile. Thematically, those passages share concepts with the creation accounts of Gen. 1-2. But can we say that Second Isaiah was envisioning a renewal of creation with the Gen. account of creation in mind?
One of the passages speaking of the transformation of the desert is in Isa. 41:17-20.
I will put in the wilderness the cedar, the acacia, the myrtle, and the olive. I will set in the desert the cypress, the plane and the pine together, that men may see and know, may consider and understand together, that the hand of the LORD has done this, the Holy One of Israel has created it.
This is reminiscent of the initial statement in Genesis about the growth of trees and other vegetation.
And God said, "Let the earth sprout vegetation, plants yielding seed, and fruit trees bearing fruit in which is their seed, each according to its kind, on the earth." And it was so.
The specific language outlining the specific types of trees that will grow in the desert is completely absent from Genesis. In fact, the writer in Genesis did not give us lists of many plants and animals. The only word that the two passages have in common is the generic word for "tree," hardly evidence of textual influence. Some writers would take the accumulation of such common words as "tree," "land," and "seed" as evidence of dependence. It seems dangerous to base such a conclusion on such meager evidence.
If textual allusions which require the transference of meaning from the source text to the target text are not sufficiently marked, the importation of meaning from another context could completely obscure the meaning of a verse.
For example, Isa. 41:19 talks about trees growing in the desert. We can take that to allude to creation. Bringing in the creation theme reminds us of the Garden of Eden which recalls the tree of the knowledge of good and evil. Recalling the tree reminds us of the forbidden fruit which reminds us of original sin.
So when the woman saw that the tree was good for food, and that it was a delight to the eyes, and that the tree was to be desired to make one wise, she took of its fruit and ate, and she also gave some to her husband who was with her, and he ate.
Reading Isa. 41 in light of the Garden of Eden account reminds us that man sinned even in the wonderfully fructified Garden through the disobedient mastication on the fruit from the tree of the knowledge of good and evil. Therefore, man will likely just make a mess of things again after the return even if God turns the desert into a fruitful garden. In a way, bringing in the Genesis context cheapens the message of redemption from Isa. 41:14 by reactivating the depression and hopelessness that Second Isaiah was trying to overcome.
There is no reason to assume that Second Isaiah intended those allusions or parallels to be drawn. The conclusions drawn by intertextuality and allusion sometimes place too much emphasis on perceived allusions that may be purely coincidental. The danger of intertextuality is that intentional use of another text is very difficult to detect in the absence of specific citations. Many of the perceived allusions could be nothing more than shared language derived from common subject matter and similar concerns.