What Tim said is right and true but I want to elaborate a little for the sake of a better understanding why. It has to do with what is known as Federal Headship.It is taught by Paul in Rom. 5:12-19, 1Cor. 15:21,22. Adam was the federal head and representative of all who were in him, that means all who are born of Adam. When he sinned it is as though we had sinned. His sin is counted as ours. Christ is the last Adam, 1Cor. 15:45. He is also the federal head and representative of all who are in Him. When He perfectly kept the Law I did in Him. When He always did that which pleased the Father I did in Him. That is what it means to be in Christ. All of the seed of Adam are born in sin. David said that he was concieved in sin. He wasn't saying that his parents were sinning when they concieved him but that he was concieved a sinner. Psa. 51:5 We read in Psa. 58:3 that the wicked, which we all are, come forth from the womb speaking lies. Sin isn't what we do it is what we are. We commit sin because we are sin. We have no ability or inclination to keep the Law or live righteously. In Heb. 2:16 we find that Christ took on the seed of Abraham not the nature of angels or the nature of Adam btw. Our sin nature comes from being born of Adam by Eve. Christ's sinless nature came from being born apart from Adam. He is the promised seed of the woman in Gen. 3:15, the seed of Abraham through whom the whole earth would be blessed in Gen. 12:3, Gal. 3:16, the promised seed of David whose kingdom is an evelasting kingdom, 2 Sam. 7:12-16 Christ Jesus the Lord is the God-Man who is able to be perfectly righteous and bring in an evelasting righteousness as a man that God will accept. Man had sinned and man must bring in righteous. Man had sinned and man must be punished. But only the God-Man could do what was required. Our Savior must be a perfect man who needs no salvation and God whom alone could do what was required.