19:12
They were not to swear falsely by the name of the Lord. Swearing falsely can be saying something that is false, but saying it as an oath, so trying to give it extra credence. Or it can be saying something claiming it is what God wants, or is consistent with His word when it isn’t. The former sort is just downright lying, and Jesus tells us to simply let our yes be yes, and our no be no. The latter are more subtle and have a veneer or religiosity, an example of this is claiming God approves of homosexuality. Examples from the past include claiming God’s word supports slavery or aprdheid. Both types profane the name of the Lord. They associate the Lord with evil in one form or another.
19:13
“Do not defraud or rob your neighbour”. This is in many ways a repeat of 19:11. All theft is robbing our neighbour, for neighbour has a wider application than just our physical neighbour, it includes anyone whom we come into contact with, directly or indirectly. There is a strong tendency within humans to defraud others, to take advantage. There is always someone who will try to do this. Holding back the wages of hired workers is forbidden. In those days the labourer needed his wages in a timely fashion (still true today!). Giving this a wider application, managers and business owners must treat their workers properly. Taking what might seem small steps to increase profits is not good.