כִּ֣י אֵ֤ל רַחוּם֙ יְהוָ֣ה אֱלֹהֶ֔יךָ לֹ֥א יַרְפְּךָ֖ וְלֹ֣א יַשְׁחִיתֶ֑ךָ וְלֹ֤א יִשְׁכַּח֙ אֶת־בְּרִ֣ית אֲבֹתֶ֔יךָ אֲשֶׁ֥ר נִשְׁבַּ֖ע לָהֶֽם׃
Porque Dios misericordioso es SEÑOR tu Dios; no te dejará, ni te destruirá, ni se olvidará del pacto de tus padres que les juró.
Rashi
לא ירפך means, He will not let loose of thee so as not to hold thee fast by His hands. The expression לא ירפך is an expression signifying: He will not cause something (our Hiphil) — He will not give thee any looseness, i.e. He will not separate you from Him. Similar is (Song 3:4) “I hold him fast, and I will not let him loose (אַרְפֶּנוּ )”, which is not vowelled אֶרְפֶּנוּ (which is Kal and an impossible form of the root רפה “to be loose”). Always the expression “letting slack (רפה)” in the Hiphil refers to one who causes looseness to others or to one who causes it to himself. For example (2 Kings 4:2) הרפה לה means, “give her looseness”; (Deuteronomy 9:14) הרף ממני means, “Give looseness to thyself from off me”.
Siftei Chakhamim
He will not cause you to be weakened, etc. I.e., the word ארפנו [erpenu], is the simple (קל), intransitive verb form. For example, “Behold, the day faded (רפה) into evening (Shoftim 19:9),” and, “Their spirit subsided (רפתה) (ibid. 8:3).” Therefore, Rashi explains that לא ירפך [yarpecha, rather than yerpecha], is the causative (הפעיל), transitive verb form. Its meaning is, “He will not cause you to be weakened.” (Re”m).