1)
What was the significance of the gifts that Avimelech sent to Avraham when he returned his wife?
1.
Rashi: It was to encourage Avraham to Daven for him, because, as HaSh-m had warned him, his very life depended on Avraham's Tefilos.
QUESTIONS ON RASHI
2)
Rashi writes: "'He gave to Avraham' - so he would be appeased, and [agree to] pray for him." But perhaps he gave these valuables to appease Sarah, and restore her honor?
1.
Gur Aryeh: If so, he should have given the gift directly to Sarah. The main reason for the gift was to encourage Avraham to pray. [Avimelech then added verbal appeasement towards Sarah, saying the money he had already given Avraham would reinstate her honor (20:16).]