15 He said to the people, “Be ready by the third day. Don’t have sexual relations with a woman.” Exodus 19:15WEB
This passage contains a positive command, qualified with a negative injunction, directed toward Israel. The positive command is: "Be ready for the third day." The negative qualifier is: "Do not have sexual relations with a women".
This is an elaboration (telescoping) on the command for Israel to sanctify themselves, given in Exodus 19:10-11.
The command was immediately fulfilled by Moses, who led the people of Israel in sanctification to prepare for the third day. The command finds its ultimate fulfillment in Jesus, who sanctifies us (Hebrews 10:8-10), and who washes us in the blood of his sacrifice (1 John 1:7), clothing us with salvation in the righteousness of Christ (Isaiah 61:10).
Notes on Interpretation/Application