1)
What will he return to his heart?
1.
Rashi: After my heart told me that I lost my hope in Hashem (18), I return to my heart that I will still hope, for "Chasdei Hashem Ki Lo Samnu
2)
Why does it say "Al Ken Ochil"?
1.
R. Yonah (Mishlei 3:26): If many afflictions came on him and he is humbled, he should trust in Hashem's mercy. He will have mercy on him due to his many afflictions, being humbled and hoping to Hashem. Perhaps this is connected to the coming verse. He hopes to "Chasdei Hashem Ki Lo Samnu Ki Lo Chalu Rachamav."
