"Under Law" in the context of Romans 6 means "under the condemnation of the law" not "without the Law". In fact Paul already argues that for the Christian our "Faith ESTABLISHES the Law of God" it does not "abolish it".
 
in Romans 6 Paul argues that violation of the Law of God shows slavery to sin.
 
Romans 6
Believers Are Dead to Sin, Alive to God
1What shall we say then? Are we to continue in sin so that grace may increase? 
2May it never be! How shall we who died to sin still live in it? 
 
4Therefore we have been buried with Him through baptism into death, so that as Christ was raised from the dead through the glory of the Father, so we too might walk in newness of life. 
5For if we have become united with Him in the likeness of His death, certainly we shall also be in the likeness of His resurrection, 
6knowing this, that our old self was crucified with Him, in order that our body of sin might be done away with, so thatwe would no longer be slaves to sin; 
7for he who has died is freed from sin.
 
 
Rom 6
8Now if we have died with Christ, we believe that we shall also live with Him, 
9knowing that Christ, having been raised from the dead, is never to die again; death no longer is master over Him. 
10For the death that He died, He died to sin once for all; but the life that He lives, He lives to God. 
11Even so consider yourselves to be dead to sin, but alive to God in Christ Jesus.
 
 
 
in Christ,
 
Bob