3 For what the law could not do in that it was weak through the flesh, God did by sending His own Son in the likeness of sinful flesh, on account of sin: He condemned sin in the flesh,
“For” explains how God achieved our freedom of verses one and two. There is a contrast here between what the law could not do and what God did do.
what the law could not do
Freedom was not achieved through the law. The Holy Spirit accomplishes what the moral law could not do. There is a weakness in the law; it could not give freedom from condemnation, justify, or impart new life. It could not do what only God can accomplish in Christ.
The definite article before “law” indicates that the law here is the Mosaic Law. The judicial basis for our liberty does not come from the Mosaic Law. The law was unable to do what it needed to do because the sin capacity could not keep those requirements. The law is impotent to justify or sanctify.
in that it [the law] was weak through the flesh,
The Mosaic Law was impotent because of the “flesh.” The flesh or sin capacity cannot deliver the believer because it could not meet the demands of the law. This was the thesis of chapter seven: the law could not overcome sin, because of the sin capacity. Even a Picasso cannot fashion a work of art on toilet paper.
The weakness of the sin capacity makes it necessary that God would intervene in the situation.
When it comes to our position before God, there is nothing that we can do for ourselves. The weakness of the sin capacity is an insurmountable obstacle to any effort to please God by the self. Our only hope is what Jesus did for us.
It is as impossible to make man righteous by the law as it is for us to measure ourselves by a false standard. Our property might be 15 yards wide and we want to build a house 25 yards wide. The standard of 15 yards can do nothing to make it possible to build a house 25 yards wide. The standard is good for measuring a standard, but it is not good for making something reach a standard. Everyone comes “short of the glory of God.” The standard for going to heaven is being as good as God is good. No one can live up to that standard. That is why we need someone to declare us as righteous as God is righteous. Jesus met the standard for us.