Your attempting to attach the Law to the Gospel.
Now, if you were witnessing to a Jew who believes in the Law then you could do what Paul did and be all things to all men to win them to Christ - key is Christ must be the Salvation from start to finish.
Not , ok now i am saved, i better obey the law now - bad.
We obviously do not obey the law in order to obtain, keep, or maintain our salvation.
But it should be clear that if we look into the perfect law of liberty and continue in it, we will be blessed in what we do (James 1:25).
Also, under the New Covenant, the law is written on our hearts and in our minds (Hebrews 8:8-10, Hebrews 10:16, Romans 8:7, Romans 8:4, 1 John 5:3, 2 John 1:6, Romans 13:8-10; Romans 5:5; 1 John 2:3-6). Therefore, will the believer in Christ not be obedient to it?
I say to you truly that in bearing the fruit of the Spirit, there is no law that will condemn us in our behaviour (Galatians 5:22-23). Thus, in bearing the fruit of the Spirit we become law-abiding citizens of the kingdom of heaven.
The righteousness of the law is fulfilled in those who walk not after the flesh but after the Spirit (Romans 8:4).
Which righteousness is not obtained by seeking to obey a set of do's and don'ts.
Thus it is a righteousness apart from the law, that is nevertheless attested to by the law and the prophets (Romans 3:21) that it is righteousness indeed.
It is the righteousness of the law that is inadvertently fulfilled in us as we do not seek to obey a set of do's and don'ts but as we, rather, place our faith in Christ and then walk according to the Spirit that He has given to us (Romans 8:4); which Spirit is the Spirit of love (Romans 5:5). Because love is the fulfilling of the law (Romans 13:8-10).
Because we receive a changed heart through faith; and because of that changed heart we walk according to His statutes and according to His judgments (Ezekiel 36:25-27). He causes us to do so (Ezekiel 36:27).