Musar zu Bereschit 25:27

ויעקב איש תם. The fact that this trait plus the fact that he was a dweller of tents, are the only ones of Jacob's many marvelous character traits that are especially mentioned in the text teaches us to what extent a person has to endeavor not to be devious and not to engage in deceit and trickery.

To sum up: Man's sins leave an imprint not only on his own face but also tarnish the "image" of G–d. This is why the Torah phrases its request that we be "perfect, whole" with Him by using the word תמים in the plural, [when it could just as well have described this attitude as תם (sing.) similarly to the Torah's description of Jacob's character in Genesis 25,27. Ed.]

When Jacob is described as יושב אהלים, "a dweller of tents," this refers to his being the link between two tents, i.e. the tent of Abraham who personified the attribute of חסד, and the tent of Isaac who personified the attribute of דין, Justice, as we have explained repeatedly. Jacob achieved a perfect blend between these two attributes. We have previously described that G–d, when He created the universe, decided to co-opt the attribute of Mercy to the attribute of Justice. Jacob reflected G–d's decision. When our sages always speak of the "love" of Abraham, the "fear" of Isaac, and the "truth" of Jacob this is the combination of Mercy and Justice. Jacob represented the emanation תפארת.