Another interpretation: "My strength" means none other than kingship, as it is said, "O LORD, the king rejoices in Your strength" (Psalms 21:2), and it says, "The LORD will give strength to His people" (Psalms 29:11), and it says, "and He will give strength to His king" (1 Samuel 2:10).
My Strength Is None Other Than the Kingdom of Heaven
Yalkut Shimoni on Torah 244:2
דָּבָר אַחֵר, אֵין עָזִּי אֶלָּא מַלְכוּת, שֶׁנֶּאֱמַר (שם כא, ב) "ה' בְּעָזְּךָ יִשְׂמַח מֶלֶךְ", וְאוֹמֵר "ה' עֹז לְעַמּוֹ יִתֵּן", וְאוֹמֵר (שמואל א ב, י) "וְיִתֶּן עֹז לְמַלְכּוֹ".