Albert Barnes Commentary Job 5:19

"He will deliver thee in six troubles; Yea, in seven there shall no evil touch thee." — Job 5:19 (ASV)

He shall deliver you in six troubles - Six is used here to denote an indefinite number, meaning that He would support you in many troubles. This way of speaking is not uncommon among the Hebrews, where one number is mentioned so that an extreme number may be immediately added. The method is to mention a number within the limit and then to add one more, meaning that in all instances the thing referred to would occur. The limit here is seven, which for the Hebrews is a complete and perfect number; and the idea is that in any succession of troubles, however numerous, God was able to deliver. Similar expressions occur not infrequently. Thus, in Amos (Amos 1:6; Amos 1:9; Amos 1:11; Amos 1:13; Amos 2:1; Amos 2:4):

Thus saith the Lord:
For three transgressions of Damascus, and for four,
I will not turn away the punishment thereof.

Thus saith the Lord:
For three transgressions of Gaza, and for four,
I will not turn away the punishment thereof.

Thus saith the Lord:
For three transgressions of Tyrus, and for four,
I will not turn away the punishment thereof.

Thus in Proverbs 30:15:

There are three things that are never satisfied,
Yea, four things say not, ‘It is enough.’

There be three things that are too wonderful for me,
Yea, four which I know not. (Proverbs 30:18)

For three things the earth is disquieted,
And for four which it cannot bear. (Proverbs 30:21)

There be three things that go well,
Yea, four are comely in going:
A lion which is strongest among beasts,
And turneth not away for any;
A greyhound;
An he-goat also;
And a king, against whom there is no rising up. (Proverbs 30:29–31)

Compare Homer, Iliad 6:174:

Εννήμαρ ξείνισσε καὶ ἐννέα βοῦς ἱέρευσεν

Ennēmar ceinisse kai ennea bous hiereusen.

An enumeration, with regard to number similar to the one before us, occurs in Proverbs 6:16:

These six things doth the Lord hate;
Yea, seven are an abomination unto Him.

No evil shall touch you - That is, permanently; for he could not mean that you would not be subjected to calamity at all, since by the very supposition you were a sufferer. But the sense is that God would save you from those calamities.