After reading from the beginning of Devarim to Shema Yisrael, the king would skip to read the second passage of the Shema - Vehaya Im Shamoa - in Parshas Eikev.
The passages read at Hakhel were designated as part of the objective of Hakhel, to inspire the people in the fear of Heaven and the observance of the Mitzvos.
Vehaya Im Shamoa represents Kabolas Ol Mitzvos - acceptance of the yoke of Mitzvos. It contains rewards for the observance of the Mitzvos and a warning for failing to observe the Mitzvos and being seduced to go astray after one’s heart to serve other gods.
Although not read at Hakhel, Parshas Eikev also contains the Parsha referred to as Parshas Hayirah - the Parsha of fear of Heaven.
Moshe calls out to Bnei Yisroel “Now Yisrael, what does Hashem your G-d ask of you? Only that you fear Hashem your G-d, to go in all of His ways, to love Him, to serve Hashem your G-d with all of your heart and all of your soul”.
These words also echo the purpose of Hakhel which was “in order... to fear Hashem your G-d and to guard to observe all of the words of this Torah”.
