The symbolism Cruz was trying to get across is pretty plain.
“Come and take it” was a challenge by Spartan King Leonidas to the Persian army during the Battle of Thermopylae when the Persians demanded the Spartans give up their arms. Texians later adopted this phrase when Mexican forces demanded the return of a cannon that they had given Texians in 1831 to fend off Native American warriors in the area. It was then being used against Mexican forces, and so they wanted it back.
The Texian response to the Mexican army’s demand was to hoist a flag made by Sarah Seely DeWitt and her daughter, Evaline. The flag was made from a wedding dress and bore the image of a lone star over the aforementioned cannon with King Leonidas’s words below it; “come and take it.”