What is the meaning of "Matan Adam Yarchiv Lo"?
Rashi: This is like the simple meaning 1 .
Rashi (citing Shemos Rabah 31:2): This refers to those who give Tzedakah. This widens his share in the world to come.
Radak #1: One who gives a gift, the land is widened for him - "Ki Atah Hirchiv Hashem Lanu" (Bereishis 26:22). He gets a reputation, and all hear about him. Wherever he goes, people appreciate him and praise him.
Radak #2: One who gives a gift, he widens his [group of] lovers. Having many lovers gives to him Shalom, and makes sadness and worry depart. Merchav is the opposite of sadness and pain - "Anani va'Merchav Kah" (Tehilim 118:5) is the opposite of "Min ha'Metzar" (ibid.)
Malbim: Unlike a Nediv, Ish Matan gives gifts also to Ashirim and Gedolim. Even though it seems that he squanders his money without need, sometimes this benefits him (refer to 18:16:2:3).
What puts a person in front of Gedolim?
Rashi (citing Shemos Rabah 31:2): Giving Tzedakah; they say about him that he is esteemed.
R. Yonah: Giving a gift gives to him honor, and puts him in front of Gedolim, for they will seek his company due to his proper deeds.
Orchos Tzadikim (Sha'ar ha'Nedivus DH ha'Nedivus): Due to his gifts, kings, officers and all people will love him.
Malbim: Giving gifts also to Ashirim and Gedolim. When he is in straits, they will remember his gifts and strive to help him.