וְעָשִׂ֥יתָ מִשְׁבְּצֹ֖ת זָהָֽב׃
און זאָלסט מאַכן אײַנפֿאַסונגען פֿון גאָלד;
Rashi
ועשית משבצת AND THOU SHALT MAKE SETTINGS — two settings, for the minimum number of settings (the plural) is two. In this section it explains to you only part of their purpose, whilst in the section dealing with the breast-plate it completes for you the explanation about them.
Chizkuni
ועשית משבצות זהב, “you are to make frames for settings of the gemstones, out of gold;” these were indentations; like miniature frames surrounding a picture which is inset. They would form the place to which the braided chains of which the Torah speaks in verse 14 and 22, could be fastened.
Rashbam
ועשית משבצות זהב, a golden plate to serve as the background to the settings which held the various gemstones of the breastplate in place. The plate had holes through which the chains could be attached to them by fastening the chains to the breastplate, as described in more detail in verse 25, the whole would in effect be as if a single piece.