“Speak to the children of Israel, saying: ‘If a woman has conceived, and borne a male child, then she shall be unclean seven days; as in the days of her customary impurity she shall be unclean. And on the eighth day the flesh of his foreskin shall be circumcised. She shall then continue in the blood of her purification thirty-three days. She shall not touch any hallowed thing, nor come into the sanctuary until the days of her purification are fulfilled.
‘When the days of her purification are fulfilled, whether for a son or a daughter, she shall bring to the priest a lamb of the first year as a burnt offering, and a young pigeon or a turtledove as a sin offering, to the door of the tabernacle of meeting. Then he shall offer it before the LORD, and make atonement for her. And she shall be clean from the flow of her blood. This is the law for her who has borne a male or a female. ‘And if she is not able to bring a lamb, then she may bring two turtledoves or two young pigeons—one as a burnt offering and the other as a sin offering. So the priest shall make atonement for her, and she will be clean.’ ” (Leviticus 12:2-4, 6-8 NKJV)
Since turtle doves mate for life they are seen as a symbol of commitment. We have the Old and New Testaments as God's commitment to man to provide a Savior for our sins and the fulfillment of that commitment.
All throughout the Old Testament, starting in Genesis 3 we find the first promise of a Savior for our sins. Every ritual, feast, the design of the temple, and the law, all point out our sinful nature and that we need a Savor to save us from our sins. The prophesies in the Old Testament tell of all the coming Savior was going to go through.
The New Testament tells of the fulfillment of those prophesies by Jesus. How He was the last sacrifice and He has saved us from our sins. That there is nothing we can do that we need Him.
I have heard people say that the Old Testament doesn't apply to today. Look at 2 Timothy 3:16-17, and write down what it says about the Old and New Testament.