אֶ֣בֶן שְׁלֵמָ֤ה וָצֶ֙דֶק֙ יִֽהְיֶה־לָּ֔ךְ אֵיפָ֧ה שְׁלֵמָ֛ה וָצֶ֖דֶק יִֽהְיֶה־לָּ֑ךְ לְמַ֙עַן֙ יַאֲרִ֣יכוּ יָמֶ֔יךָ עַ֚ל הָֽאֲדָמָ֔ה אֲשֶׁר־יְהוָ֥ה אֱלֹהֶ֖יךָ נֹתֵ֥ן לָֽךְ׃
Pesas cumplidas y justas tendrás; epha cabal y justo tendrás: para que tus días sean prolongados sobre la tierra que SEÑOR tu Dios te da.
Rashi on Deuteronomy
אבן שלמה וצדק יהיה לך THOU SHALT HAVE A PERFECT AND JUST WEIGHT — This again suggests: if you will do this, (using just weights and measures), you will have (יהיה לך) much (cf. Sifrei Devarim 294:3).
Rashbam on Deuteronomy
שלמה וצדק, one single chunk, (not composites) true and fair.
Rabbeinu Bahya
אבן שלמה וצדק יהיה לך, “a perfect and honest weight you shall have.” If you make sure to have honest weights, and your business will be based on fairness you will have alot, i.e. יהיה לך [as opposed to the previous לא יהיה לך, Ed.].