16:18 O earth, do not cover my blood- The earth is sometimes called to witness men’s sins (Deut. 30:15-20; Isa. 1:2; Micah 6:1-2) but here Job calls upon it to testify of His innocence. 

Job’s longs for the earth not to cover his blood. The phrase cover his blood also appears in Gen. 37:26; Isa. 26:21. In Gen. 4:10 the voice of Abel’s blood cried out from the ground. Blood represented life itself (Lev. 17:11), and it is precious. Even an animal’s blood was to be covered with the ground (Lev. 17:13; Ezek. 24:7-8). Because life and blood were so precious, taking life demanded one’s life be taken (Gen. 9:5-6; Num. 35:29-34). 

And let there be no resting place for my cry- The law of Moses made provision for an avenger of blood who executed the killer of his near kin (Num. 35:9-34). If the avenger failed to act, God was expected to act. Job begs that his cry find no resting place until he was avenged. 

16:19 Even now, behold, my witness is in heaven,- While Job’s appearance served as a witness against him in vs. 8, he is confident of a witness in heaven (vs.19). The witness is more than just a man. He is in heaven.

But who is this witness, this advocate? Some argue that the witness is God Himself.[1] In this context, the witness seems like a 3rd party who will plead his case before God (vs. 21). 

And my advocate is on high- The word translated advocate is only used here. 

 16:20 My friends are my scoffers;- There is question about the translation of key words. 

The word translated friends is used of Job’s friends in 2:11; 32:3; 42:10.

The NET translates this phrase “My intercessor is my friend.” This word translated intercessor can carry the idea of scoffer (Ps. 1:1; Prov.1:22; 3:34; 9:7, 8, 12; 13:1; 14:6) or it can speak of a translator or an interpreter (Gen. 42:23; II Chron. 32:31; Job 33:23; Isa. 43:27).[1] 

[1] Newsome, 460-461, does not believe these words variously translated are from the same Hebrew word but that they are different words. Clines, 371, agrees and has some good notes about the translation. 

Jesus and Job 16:15-22

16:16, 20 Job’s face is flushed with weeping. Jesus wept at the tomb of Lazarus (John 11:35), at the triumphal entry to the city of Jerusalem (Luke 19:41-44), and at Gethsemane (Heb. 5:7). Jesus offered strong crying and tears to the One able to save Him. 

 16:17 Job was innocence and there was no violence in his hand. Jesus was completely innocent and there was no violence in His mouth on a much greater level than Job (Isa. 53:9; I Peter 2:22). 

 16:18 Job begs that the earth not cover his blood. While the blood of Abel cries out for vengeance, the blood of Jesus cries out for mercy (Gen. 4:10; Heb. 12:24).

 16:21 Compare this to Job 9:32-33; 19:25; 33:23-24. Job is not prophesying of Jesus in the sense of stating what He will do. Job is expressing a longing, a desire for One who will do what Jesus accomplishes. Jesus actually goes far beyond what Job desired. Job’s sins, however small, had made him God’s enemy (Rom. 5:6-10). All the things Job experienced, and more were endured by Jesus on the cross to bring those who were His enemies back to Him.