Mishnah Berachoth 2.2
2) Rabbi Joshua ben Korchah said:
a) Why was the section of “Shema” placed before that of “And it shall come to pass if you listen“?
i) So that one should first accept upon himself the yoke of the Kingdom of Heaven and then take upon himself the yoke of the commandments.
EXPLANATION: the passage “Shema Yisrael, … [Devarim 6.4]” precedes “Vehayah im shamoa… [Devarim 11.13]” because “accepting G-D’s Sovereignty logically precedes the acceptance of His dictates. Only one who views himself as a subject of the King will obey His Commands.“
(Yad Avraham Artscroll Mishnah Series, Berachoth Seder Zeraim, page 109, Chapter 2: Hayah Korei)