"And also I have established my covenant with them, to give them the land of Canaan." (6:4)
R' Yosef Yaavetz (1435-1507; known as "R' Yaavetz heChassid") questions the use of the conjunction "And also." Usually, he notes, "also" is used to connect two "positive" or two "negatives," but here it connects a "positive" ("I have established") to a "negative" ("I did not make Myself known").
R' Yaavetz explains that the two verses are actually parallel. Both teach that sometimes events are determined by the level where the protagonist stands, and sometimes by other considerations.
For example, the Patriarchs never saw Hashem behave in the way represented by His four-letter Name (which we pronounce "Hashem"). However, this was not because the Patriarchs were not on the appropriate level; rather, history was not prepared for such involvement by Hashem.
Similarly, Hashem told Moshe, when it comes to fulfilling My covenant with the Patriarchs, you must understand the difference between what I choose to do and what history calls for. I will fulfill my covenant with the Patriarchs, even though Bnei Yisrael are not presently worthy. However, this requires them to undergo the additional suffering about which you have questioned Me (as described at the end of last week's parasha).