The reason is given for the precept Proverbs 23:10.
Their redeemer - See Job 19:25 note. It was the duty of the גאל gā'al, the next of kin, to take on himself, in case of murder, the office of avenger of blood Numbers 35:19. By a slight extension the word was applied to one who took on himself a like office in cases short of this. Here, therefore, the thought is that, destitute as the fatherless may seem, there is One who claims them as His next of kin, and will avenge them. Yahweh Himself is in this sense their גאל gā'al, their Redeemer.

For their redeemer is mighty - גאלם goalam, their kinsman. The word means the person who has a right, being next in blood, to redeem a field or estate, alienated from the family, to avenge the blood of a murdered relative, by slaying the murderer; and to take to wife a brother's widow, who had died childless, in order to preserve the family. The strength here mentioned refers to the justness of his claim, the extent of his influence, and the powerful abettors of such a cause. But in reference to the orphans here mentioned, they having no kinsman, God takes up, vindicates, and avenges their cause.

For their Redeemer is mighty,.... As he must needs be, since the Lord of hosts is his name; who sympathizes with them, has mercy on them, is their father, and their friend; see Jeremiah 50:34;
he shall plead their cause with thee; or "against thee", as the Vulgate Latin version; and will certainly carry it for them, and against thee; for, when he undertakes a cause, he pleads it thoroughly.

redeemer--or avenger (Leviticus 25:25-26; Numbers 35:12), hence advocate (Job 19:25).
plead . . . thee--(Compare Job 31:21; Psalm 35:1; Psalm 68:5).

Redeemer - Hebrews. their near kinsman, to whom it belongs to avenge their wrongs, and to recover and maintain their rights.