To show that JESUS is both the sin offering and peace offering and as an added bonus He is also the Prince of Peace.
Do you need two to save you from sin and acquire peace?
No. Only JESUS CHRIST is needed.
2 Peter 3:14 (Amplified Bible)
So, beloved, since you are expecting these things, be eager to be found by Him [at His coming] without spot or blemish and at peace [in serene confidence,