Why those Avraham make his servant swear with his hand under Avraham’s thigh? The "thigh" (or "loins") was a euphemism for the reproductive organs, signifying an oath sworn by the very source of future generations and God's covenant, making it incredibly serious, much like swearing on one's "seed" or lineage, or at least that is what is believed; Scripture does not say.

“I will make you swear, in YHVH, (who is) the Powers of heaven, and (who is) the Powers of the land/earth.”

     By now, I hope you do not wonder why I say "powers" rather than just "God". If you, by chance, came here, to this specific page, you have to go back to the beginning and read and understand this. God is “EL”, and Gods is “Elohim”, in Hebrew, “EL” means Power and “Elohim” means powers with no other language in between, from Hebrew to English. The word "God" comes from Germanic languages and means "deity," any deity. YHVH is where all powers in existence come from, even your power, meaning your existence. Without Him, we would not be alive. So, who is YHVH? All the powers of heaven and all the powers of the world. To say it in today’s language, YHVH is God over heaven and God over all the earth. In this verse, when it comes to who God is over heaven and earth, only His sacred name is mentioned, and no one else.

“that you will not take a wife for my son from the daughter of the Kenanites, with whom I dwell among them.”

     I am not going to pretend that I know the reason why Avraham was so opposed to marrying Yitzkhak to a woman of the land. However, you could say that the women of the land did not believe in YHVH and were too rooted in their traditions of other gods. This is a habit too strong to break. Religious tradition is deeply rooted in family memories. However, we must also remember that this is why YHVH took Avraham away from his family and land: he was the only one who believed in YHVH alone, according to the rabbis. So, there is no warranty of the woman from his land to believe the same as Avraham’s family, from Avraham’s perspective, that is. I can also say that Avraham did it because that is the Law of YHVH, spelled out but not written word-for-word in Deuteronomy 7:3-4. In simple terms, a person born to a Jewish mother, no matter the father, is a Jew, but a person born to a Jewish father, but the mother is not Jewish, the baby is not Jewish; therefore, the baby, when it grows up, must convert into the Jewish family. You may ask, then what is the father to the child? The father signifies the baby's tribe or lineage, but does not make the baby Jewish. However, the Law had not been given at the time of Avraham, and I do not think that Avraham could have found a suitable woman for Yitzkhak among the women of the land of Canaan, at least one who was modestly wise. Maybe this is the reason why the Torah explains here the state of Avraham’s old age. Avraham might have been stubborn and difficult in his old age. Do we know for sure Avraham’s reasons? No, we do not. One other thing that comes to mind is that Avraham may know that the Khanaanites are descendants of Kham, Noakh’s son, who was cursed by his father for what he did, and Avraham is a descendant of Shem, Kham’s older brother. Shem was blessed, and Kham was cursed. So, Avraham does not want his son to marry a cursed woman.

     Another question: why ask this of his servant and not just tell Yitzkhak? Couldn’t it be more obvious that Yitzkhak has gone his own way, apart from Avraham? And also, Avraham made him promise that he, his servant, would not get a wife for Yitzkhak from the Canaanite woman. Like if it was the servant’s duty to do this after he is dead. One other thing we have to understand is that Avraham was old and most likely could not make a long journey anymore. He is either stuck where he is or does not want himself or Yitzkhak to leave Canaan, the land promised to him and his descendants.

     Ibn Ezra (approximately 1089 - 1092 to approximately 1164 - 1167) commentary:

PUT, I PRAY THEE, THY HAND UNDER MY THIGH. Some say that my thigh alludes to Avraham’s circumcised member. However, if this were the case, Avraham should have had him swear by the covenant of circumcision, not by the Lord. I believe that it was customary in those days for a person to place his hand under the thigh of his master, its meaning being, “If you are subject to my authority, place your hand under my thigh.” The lord then sat on his servant’s hand. By doing so, the servant, as it were, said to the master, “My hand is under your authority to do your will.” This custom is still followed in India.

OF THE CANAANITES. This includes all of the eleven Canaanite peoples.

     Chizkuni (13th Century) commentary:

“The senior servant of his household,” his servant was old enough so that Avraham did not have to worry that he would take advantage of his position to indulge in incestuous conduct.

תחת ירכי: according to the plain meaning of the word, it has nothing to do with the place where Avraham circumcised himself, although it was the most sacred part of his body. If it had, why did Avraham not make him swear an oath by using it as the focus instead of using Hashem as his focus? It simply was the custom in those days that any person who was subservient to another person would place his hand under the thigh of his master as a symbol that he acknowledged him as such. Having done this was equivalent to a promise to carry out his master’s wishes. This custom was still in use in India in our author’s time.

Kli Yakar (כלי יקר), meaning "precious vessel," refers to a popular Torah commentary written by the Polish rabbi Shlomo Ephraim ben Aaron Luntschitz (1550-1619). Commentary:

Among whom I live. If Yitzchok lived near his wife’s family, either in Canaan or in Charan, he would be subject to their influence. But if he married a woman from Charan and they lived in Canaan, he would not be influenced by them.

     Or HaChaim (approximately 1696 - 1743) commentary:

"among whom I dwell." Abraham countered his servant's assumption that, inasmuch as the very proximity of Abraham causes one to be included in the blessing G'd promised to Abraham, this did not mean that one's basic status of being cursed (as a result of Noach's curse) had been revoked. Abraham also wanted to dispel the notion that his presence and status among people such as Aner, Eshkol, and Mamre would be endangered if he did not take a wife for Isaac from their families.

     Rabbeinu Bahya (1255 – 1340) commentary:

“that you will not take a wife for my son from amongst the daughters of the Canaanite, etc.” He warned his servant not to take a wife from a cursed nation. When a woman is predestined for destruction, she is apt to drag her husband in the same general direction. This is precisely what the mother of all human beings did (compare Genesis 3:20). You are aware that this is what happened to Solomon, who married a number of alien women (Kings I 11:1). The prophet testifies there that it was these women who turned his heart from being completely loyal to G-d. This is the reason that it has become the custom of the Jewish people to read this portion (in the presence of the assembled guests) to a bridegroom on the day he marries, to remind all the people to be very circumspect in their choice of life-partners. Proverbs 31:30, “grace is deceptive, and beauty is vain.“ He should also not marry a woman because she is wealthy, as money is apt to develop wings and to fly off just like an eagle (compare Proverbs 23:5). The groom should also not marry a woman because she is a member of a powerful and influential family, and he hopes to become powerful and influential himself due to his wife’s connections. If these are a groom’s considerations in the choice of his wife, he will be punished and will likely fail on all three counts. The guiding considerations when choosing a wife are reverence for G-d and a desire for a family with a good reputation. Seeing that, in the majority of cases, the daughter‘s character is similar to that of her brothers, one may form some idea of what a girl is like by observing how her older brothers conduct themselves.
Our portion also teaches that it is appropriate to select a bride from amongst one’s family, as did Avraham (compare verse 4) for his son Yitzchak, and as did Amram, who married Yocheved (an aunt, Exodus 2:1 something that the Torah forbade later on. Whenever people marry someone to whom they already have a natural affinity, such as members of their own family (excluding incest, of course), the likelihood of harmonious relations not only between husband and wife but between the mutual members of the respective families is enhanced.
If someone marries a wife from a lower social stratum, there is a chance that he will feel superior to her, and this will lead to bad blood and resentment on his wife’s part. The result will be ongoing friction. Our sages in Pessachim 49 have described families who are cleaving to one another because they are all part of the same social strata as ענבי הגפן בענבי הגפן דבר נאה ומתקבל, “grapevines joining grapevines are something beautiful and acceptable.” The author continues in this vein, concluding with the quotation from Psalms 125:4 הטיבה ה’ לטובים ולישרים בלבותם, “Do good, O Lord to the good, to the upright in their heart.” The psalmist implores G-d to grant His blessing to people whose motivations in their choice of wife are guided by the principles we have just outlined. The psalm goes on by predicting that those who are guided by base motivations will join the path of the evildoers. When such clear lines of distinction are drawn between people who are sincere in their motivations and those who are not, Israel will be at peace (as one will not confuse one group with another).

     Radak (1160-1235) commentary:

ואשביעך..ואלוקי הארץ, meaning that the same G’d Who is ruler in the heavens also exercises His control down here on earth. Do not think that if you do not honour an oath made to G’d in heaven, failure to honour it would not have negative consequences for you here on earth. When Avraham speaks of his own self, as opposed to the need to make someone else take an oath, he only needs to refer to the “G’d of the heavens” (compare verse 7). Avraham was well aware of G’d being also the G’d on earth. In Bereshit Rabbah 59:8, Rabbi Pinchas is quoted as saying that until He revealed Himself to His creatures, G’d was known only as the “G’d of the heavens,” whereas after He revealed Himself to His creatures [or to an individual creature by performing a miracle for such a person Ed.] He also became known as the ”G’d of the earth.”

מבנות הכנעני, for the entire Canaanite tribe is cursed since the days of Noach, and Avraham’s seed is not to be merged with that of a cursed tribe.