The English word translated as "jewels" in verse 17 is not entirely wrong, but it is not a precise translation of what the Hebrew word, segullah (Strong's #5459, transliterated in various ways), really means. The simplest usage of segullah is to indicate personal possession. Vine's Expository Dictionary of Biblical Words expounds its meaning (remember that we are being described):
Cegullah signifies property in the special sense of a private possession one personally acquired and carefully preserves. Six times this word is used of Israel as God's personally acquired (elected, delivered from Egyptian bondage, and formed into what He wanted them to be), carefully preserved, and privately possessed people. . . .
This is not the first time this word appears in the Bible, which distinction belongs to Exodus 19:5, "Now therefore, if you will indeed obey My voice and keep My covenant, then you shall be a special treasure to Me above all people; for all the earth is Mine." Segullah is translated as "special treasure."
The Keil and Delitzsch Commentary explains:
This manifestation of the love of God to Israel formed only the prelude, however, to that gracious union which Jehovah was now about to establish between the Israelites and Himself. If they would hear His voice, and keep the covenant which was about to be established with them, they should be a costly possession to Him out of all nations. . . . Cagulaah does not signify property in general, but valuable property, that which is laid by, or put aside, hence a treasure of silver and gold. . . .
It is helpful to note how God emphasizes segullah to impress its importance on Israel—and now us—by saying, "For all the earth is Mine." This establishes a reference point, indicating that He could have considered any people on earth as His own personal and private treasure, but He did not. Just as a person carefully and discriminately chooses his personal jewelry according to his own criteria, so He chose Israel then and chooses us now.
In I Chronicles 29:3, segullah is again translated as "special treasure," but the context provides a clear use of the term. It involves the preparations David made for the building of the Temple so Solomon could construct it. David explains that from his own personally obtained and set-aside treasure, he gave so much gold and silver.