Comentario citado sobre I Samuel 3:14

and I swore to you (Exod. 6: 6): “Therefore (לָכֵן), say to the children of Israel: I am the Lord! I shall take you out, etc.” “Therefore” means only an [introduction to an] oath, as it is said (I Sam. 3:14): “therefore, I have sworn to the house of Eli...”

לכן לא תביאו, “therefore you will not bring, etc.” Whenever the expression לכן, appears, it indicates that the speaker is saying something in the nature of an oath. Compare: Samuel I 3,14: לכן נשבעתי לבית עלי, “therefore I have sworn concerning the house of Eli;” compare alsoDeuteronomy 4,21: וישבע לבלתי עברי, “therefore He swore that I may not cross, etc.”If you were to query that we read at the end of Exodus 6,7 that Rashi explains the words: עתה תראה, “now you will see,” that Moses, while witnessing the Exodus from Egypt, will not witness the crossing of the Jordan into the land of Canaan, (as a penalty for having questioned G-d’s handling of the Israelites since his appointment as their leader) he had already forfeited the right to cross into the land of Israel 40 years earlier, so what is new about G-d’s oath here? We may answer that both incidents combined to deny him entry to the Holy land; [alternately, in Exodus, the matter had only been hinted at, (thus preventing Moses from apologizing and doing teshuvah) and had not been confirmed by G-d with an oath thus making it irrevocable. Ed.].

לכן לא תביאו, “therefore you will not bring, etc.” Our sages in Pessikta Zutra claim that the expression לכן always denotes a statement equal in force to that of an oath. We find this word introducing G’d’s oath to punish the descendants of the house of Eli in Samuel I 3,14: “Therefore I have sworn, etc.” In our verse it means that G’d swore that neither Moses nor Aaron would enter the Holy Land. This is the reason why the paragraph is followed immediately by Moses sending messengers to the King of the Edomites to let the Israelites pass his country on their way to the Holy Land. In Kadesh Moses had forfeited his right to enter Eretz Yisrael and it was from there that he sent emissaries.

לכן לא תביאו THEREFORE YE SHALL NOT BRING — This expression (“therefore”) is used by way of an oath, just as (I Samuel 3:14), “Therefore I have sworn to the house of Eli”. Here He was quick to take an oath in order that they should not pray at length about it (that He should withdraw the decree) (Midrash Tanchuma, Vaera 2).