Was Jesus’ Death Really a Sacrifice if He Knew He Would Rise Again?

Questions about why God the Father required a sacrifice (and whether Jesus’ short-term death was really a sacrifice), whether Jesus’ disciples ever offered sacrifices at the temple, and what it means to say that sin causes separation from God if God is omnipresent.

• Why did God the Father require a sacrifice, and if Jesus knew he would rise again in three days, was his death really a sacrifice?
• Did Jesus’ disciples ever offer sacrifices at the temple, and if not, why not?
• How can I explain the idea that “sin causes separation from God” to someone who believes that it denies God’s omnipresence and denies Jesus interacted with sinners?