Remove not the old landmark; and enter not into the fields of the fatherless:
The Lord of heaven and earth protects property rights. He especially protects the poor and helpless. It is tempting to alter assumed business practices for financial advantage, but God condemns such acts. It is tempting to take financial advantage of those who cannot defend themselves, but God condemns that as well. He will come to the aid and defense of those victims, and you will wish you had stayed away (Pr 23:11; 22:22-23).
It was customary in Bible times to use a pile of stones, post, or other marker to establish property boundaries. These landmarks would remain unmoved from one generation to the next, as property continued as part of family estates. God gave wonderful laws to Israel under Moses, and one of them was the protection of property rights by condemning the moving of these landmarks (Pr 22:28; Deut 19:14; 27:17; Job 24:2; Hos 5:10).
The fatherless are those who had lost their fathers to war or early death. They lacked a strong male defender for property protection or business transactions. Entering into their fields by any means of encroachment or theft was a heinous offence. The principle would obviously apply to other acts of property theft as well, such as misdirection of water, grazing of their fields, stopping of their wells, breeding of your herds, and so forth.
Like widows, God took special care of the fatherless, foreigner, and poor (Jer 22:3; Zech 7:10). The mighty God promised to come from heaven with vengeance on those who trouble these two categories of the weak and helpless (Job 31:21-23; Ps 94:6; Eccl 5:8; Mal 3:5). It is wisdom and true religion to go out of your way to help both (Jas 1:27)! Never ask more than market price or pay less than market price to any of these parties.
The rule for property boundaries applies to all economic transactions and business practices. You have no right to alter any established way of doing things unless all parties are fully agreed and there is no damage at all to others. God demands impeccable honesty and integrity in all property transactions. There is no room for compromise or confusion. He will avenge harshly! Do you go out of your way financially to honor the poor? You will never lose in such decisions, for the God of heaven will repay you well (Pr 19:17).
There is a spiritual application. Men today alter God's worship to make it acceptable to the world. They call it casual, contemporary, purpose driven, or seeker sensitive. They are removing old landmarks (II Thess 2:15). But the Lord calls you to seek the old paths (Jer 6:16). He calls you to earnestly contend for the old faith (Jude 1:3). Turning from sound doctrine to entertainment and fables is a mark of perilous times (II Tim 3:1 - 4:4).