About 1/3 of the verses in the NT contain quotes or allusions to the OT in order to establish that it supported what they were saying and to show that they hadn't departed from it, so they kept going back to the OT and you shouldn't have a problem with that.
Grace is not something new in the NT in opposition to God's righteousness in the OT, but rather graciousness and righteousness have always been compatible character traits of the same God that he expressed throughout both the OT and the NT (Exodus 34:6-7). Again, Psalms 119:29-30 shows that God was gracious to David by teaching him to obey His law. In Exodus 33:13, Moses wanted God to be gracious to him by teaching him His way that he might know Him and Israel too, in 1 Kings 2:1-3, God taught how to walk in His way through His law, and in John 17:3, eternal life is knowing God and Jesus, which again is salvation by grace through faith. In Romans 1:5, we have received grace to bring about the obedience of faith, and in Titus 2:11-14, our salvation is described as being trained by grace to do what is godly, righteous, and good, and to renounce doing what is ungodly, so God graciously teaching us to obey His law is itself the content of His gift of salvation, which is not something that is different in the NT, so you are the one who has no concept of grace.
The Mosaic Law teaches us how to act in accordance with the nature of the God of Israel, and the only way that the New Covenant could involve following a different set of laws would be if it were made with a different God with a different nature, but rather the New Covenant still involves God putting the Mosaic Law in our minds and writing it on our hearts. Changing the medium upon which the Mosaic Law is written from stone to our hearts does not change the content of what it instruct us to do, such as the command to honor our parents written on stone has the same content as the command to honor our parents written on our heart. The New Covenant involves God protecting the Mosaic Law by writing it on our hearts so that we will obey it, not so that we will have justification for rejecting it.
Furthermore, the Spirit has the role of leading us to obey it (Ezekiel 36:26-27). The Spirit is not in opposition to the Father, so you have given no justification for thinking that the Law of the Spirit is something different than or contrary to what the Father has commanded. The freedom that we have in Christ is the freedom from sin, not the freedom to do what God has revealed to be sin through His law. In Psalms 119:142, the Mosaic Law is truth, and in John 8:31-36, it is sin in transgression of the Mosaic Law that puts us in slavery while it is the truth that sets us free, not the other way around.