Bava Kama 17a: Sow for yourselves Tzedakah; you will reap according to the Chesed (that Hashem will do for you).

Rashi: However, you plowed evil - therefore "destruction will come upon your nation" (14).

Radak: Do what is good in My eyes, and the good reward you will receive from Me will be greater than your good deeds, just like one who sows a Se'ah hopes to reap two Sa'im or more. It mentions seeding with Tzedakah and reaping with Chesed, for Chesed is greater than Tzedakah. Sukah 49b learned this from our verse. One who seeds, it is a Safek if [it will produce and] he will eat. One who reaps, surely he will eat!

Radak citing his father: All that you harvest in this world, it will be Chesed until you will come to the world to come, and He will show to you the principal. So Chazal said, that there are several Mitzvos that one eats their Peros in this world, and the principal is intact for the world to come (Pe'ah 1:1).

Orchos Tzadikim (Sha'ar ha'Nedivus DH Kelalo): This is one who does Tzedakah, and there is Chesed with it. E.g. he buys with coins something that an Oni needs, lest the Oni need to toil to buy it. Or, he finds a low price for what an Oni needs, and the Oni lacks money to buy it; he is meticulous to give to him then.

Malbim: Then you will seed Tzedakah and good deeds in Mitzvos Bein Adam la'Makom, you will reap according to Chesed. Just like from one seed, you reap bundles, so the reward you will receive is according to Hashem's Chesed is more than is proper according to Emes and Mishpat. Rather, it is Chesed, which has no limit or measure.

Rashi #1: Engage in Torah, and from there you will learn to go in the good path to overpower the Yetzer ha'Ra. This is like one who plows a field to overturn roots of summer grass that weakens grain.He plows several days before seeding.

Rashi #2: Do good deeds before the pressure will come against you. This will cause your prayers to be accepted at a time of need. Then it will be a proper time for you to seek Hashem for all your needs - He will hear your screams, and cast Tzedakah to you. Yoreh is like "Yarah va'Yam" (Shemos 15:4).

Radak #1: After you reap, plow again. All your days, do not cease your good deeds! Nir is plowing. The Targum of "v'Lacharosh Charisho" (Shmuel I, 8:12) is Leminar Nirei. Chazal said 'if he made a Nir (plowed but did not seed) one year, and seeded it one year' (Bava Basra 36b).

Radak #2: This is a Mashal to arouse hearts to accept words of rebuke, just like plowing a field makes it receive seed. Niru is a command, in Hif'il conjugation. It should say Haniru; the Hei is omitted, like normally occurs in commands when the middle letter of the root is silent, e.g. "Simu" (Bereishis 43:21), "Shisu" (Tehilim 48:14).

Malbim: Nir is plowing deep, to remove thorns that ruin grain. So you will plow deep in the Nefesh to remove desires and evil images and false Emunos that ruin the seed of Tzedakah and good deeds.

Rashi: When you will fix a time to seek Hashem to learn Torah - when you will exert in it, He will make you understand to inform you of its hidden matters in Tzedek.

Radak citing Targum Yonasan: At all times [the Navi tells you to return to fear Hashem].

Radak citing Ibn Ezra: When you seek Hashem, then the Malkosh (late rain) will come and Yoreh Tzedek for you. Yoreh is like "Yoreh u'Malkosh" (Devarim 11:14).

Radak: If you will seek Hashem to know His Torah and Mitzvos, He will come and teach to you Tzedek - 'one who comes to purify himself, [Shamayim] helps him' (Yuma 38b).

Malbim: After they will prepare the plowing and seeding, the time of rain will come. One must seek Hashem that He give rain, Yoreh and Malkosh in their times. I.e. they must request from Him a Heavenly influence and Divine help from above. The Tzedek that He will send to you is the rain. This does not refer to the ground, like the simple meaning, rather, the ground of your Nefesh. He will satiate your thirsty Nefesh with rain of His strength and Kadosh influence - "Har'ifu Shamayim mi'Ma'al u'Shchakim Yizelu Tzedek" (Yeshayah 45:8).