en_tn/jol/02/23.md

he will ... bring down showers for you

"he will ... cause much rain to fall so that you will live well"

he will give you the autumn rain as vindication

Possible meanings are that Yahweh will give the rain 1) to show that he is faithful to the Israelites or 2) to show that the Israelites were right to trust Yahweh.

autumn rain and the spring rain

the first rains of the rainy season in early December and the last rains in April and May