Musar su Abacuc 2:4

Therefore, all of the Torah is completely enclosed in faith, as it is written, "But the righteous shall live by his faith" (Hab. 2:4). And concerning Abraham, it is said : "And he believed in the Lord and He counted it to him for righteousness" (Gen. 15:6). And concerning all other good qualities such (a reward) is not written in Scripture.

When such semen has been used in sleeping with a married woman (other than his wife), and a child is the result of such a union, it cannot become part of the Jewish nation, but is a Mamzer since it represents a denial of the father's covenant with G–d, and is the quintessence of impurity. The issue of such a union would certainly not be provided with a נפש originating in a region of purity.

As there are 70 ways to explain the Torah, we are are permitted to approach these problems from a different angle. We will do so by referring to a different Midrash. Commenting on Song of Songs 4,8: תשורי מראש אמנה, Tanchuma Beshalach 10 states that the redemption of the Jews was triggered by G–d's knowledge that they would compose the song of gratitude and extol G–d's virtues as recorded in our portion. In turn the merit that enabled Israel to proclaim this song originally was Abraham's for he had expressed faith in G–d as reported in the Torah (Genesis 15,7) that he believed the promise that he would have children and that their children would inherit the land of Canaan.