James 5 has a seeming disconnected series of exhortations, which seems to come to a culmination of sorts, Before, above, more than everything brothers: Do not swear ….James 5:12. The connection between care for the poor, a metaphorical discourse as to the harvest & a command to not swear may have been suggested by the commands of Leviticus 19:9-18:
9 “When you reap the harvest of your land, you shall not reap your field right up to its edge, neither shall you gather the gleanings after your harvest.
10 And you shall not strip your vineyard bare, neither shall you gather the fallen grapes of your vineyard. You shall leave them for the poor and for the sojourner: I am the LORD your God.
11 “You shall not steal; you shall not deal falsely; you shall not lie to one another.
12 You shall not swear by my name falsely, and so profane the name of your God: I am the LORD.
13 “You shall not oppress your neighbor or rob him. The wages of a hired servant shall not remain with you all night until the morning.
14 You shall not curse the deaf or put a stumbling block before the blind, but you shall fear your God: I am the LORD.
15 “You shall do no injustice in court. You shall not be partial to the poor or defer to the great, but in righteousness shall you judge your neighbor.
16 You shall not go around as a slanderer among your people, and you shall not stand up against the life of your neighbor: I am the LORD.
17 “You shall not hate your brother in your heart, but you shall reason frankly with your neighbor, lest you incur sin because of him.
18 You shall not take vengeance or bear a grudge against the sons of your own people, but you shall love your neighbor as yourself: I am the LORD.
Compare the combination of commands with the series of commands in James 5:
1 Come now, you rich, weep and howl for the miseries that are coming upon you.
2 Your riches have rotted and your garments are moth-eaten.
3 Your gold and silver have corroded, and their corrosion will be evidence against you and will eat your flesh like fire. You have laid up treasure in the last days.
4 Behold, the wages of the laborers who mowed your fields, which you kept back by fraud, are crying out against you, and the cries of the harvesters have reached the ears of the Lord of hosts.
5 You have lived on the earth in luxury and in self-indulgence. You have fattened your hearts in a day of slaughter.
6 You have condemned and murdered the righteous person. He does not resist you.
7 Be patient, therefore, brothers, until the coming of the Lord. See how the farmer waits for the precious fruit of the earth, being patient about it, until it receives the early and the late rains.
8 You also, be patient. Establish your hearts, for the coming of the Lord is at hand.
9 Do not grumble against one another, brothers, so that you may not be judged; behold, the Judge is standing at the door.
10 As an example of suffering and patience, brothers, take the prophets who spoke in the name of the Lord.
11 Behold, we consider those blessed who remained steadfast. You have heard of the steadfastness of Job, and you have seen the purpose of the Lord, how the Lord is compassionate and merciful.
12 But above all, my brothers, do not swear, either by heaven or by earth or by any other oath, but let your “yes” be yes and your “no” be no, so that you may not fall under condemnation.
While the relationship is not exact, there are numerous points of correspondence. If James did rely upon Leviticus, the importance of swearing makes sense: to swear falsely is to profane the name of The Lord (Lev.19:12). Both passages directly tie reverence of The Lord to love of neighbor. That relationship must not include deceit, injury or fraud (resulting from false swearing).