Recently I have been learning about covenant theology and have come to see that the gospel realities in the NT are present also in the OT. This definitely changes how I read the OT. It makes sense of appeals in the NT to the OT like in 1 Corinthians 10:1-10. However, as I've been reading other writers I've been confused by their appeal to the OT; the things they mention don't seem to be about the substance of the covenant of grace and I'm not sure how I'd convince my friends that they relate to the character of God. I'm trying to understand why they can appeal to the OT in the below examples? Perhaps the issue is knowing how to distinguish between things that are peculiar to the administration of the covenant of grace and those which are "universal truths".
Example 1 (Worship): To justify the regulative principle most people will go to Leviticus 10 and refer to the story of Nadab and Abihu where they offered strange fire which God had not commanded and God struck them. From this they argue that we see that worship not commanded by God is forbidden.
Example 2 (Ecclesiology): it is argued here that lay persons should not usurp and interfere with ministers. The argument is made from an appeal to the story of Korah in Numbers 16 and Uzzah in 2 Samuel 6 and Uzziah in 2 Chronicles 26 where all of these people are punished because they usurped the offices that God had ordained.
Why do the above arguments from the OT apply to us now in the new covenant? It could be argued that they do not relate to God Himself or the gospel, but how God related to His people in the old covenant administration. I am aware that arguments can be made for the RPW from the NT or even the 10 commandments which are still binding, but this then forms the basis for why we use the RPW, not the OT and so appeals to the OT are unnecessary. Perhaps the above arguments are sound because unless something is revoked in the NT we should not think that God has revoked it. But the above could be, perhaps poorly, argued to be strictly related to something that has been revoked; namely the ceremonies or the Levitical priesthood.
Question: On what basis can we appeal to the OT to justify doctrine and practice that does not directly relate to God's character or the gospel? E.g. in the realm of worship and ecclessiology.
Example 1 (Worship): To justify the regulative principle most people will go to Leviticus 10 and refer to the story of Nadab and Abihu where they offered strange fire which God had not commanded and God struck them. From this they argue that we see that worship not commanded by God is forbidden.
Example 2 (Ecclesiology): it is argued here that lay persons should not usurp and interfere with ministers. The argument is made from an appeal to the story of Korah in Numbers 16 and Uzzah in 2 Samuel 6 and Uzziah in 2 Chronicles 26 where all of these people are punished because they usurped the offices that God had ordained.
Why do the above arguments from the OT apply to us now in the new covenant? It could be argued that they do not relate to God Himself or the gospel, but how God related to His people in the old covenant administration. I am aware that arguments can be made for the RPW from the NT or even the 10 commandments which are still binding, but this then forms the basis for why we use the RPW, not the OT and so appeals to the OT are unnecessary. Perhaps the above arguments are sound because unless something is revoked in the NT we should not think that God has revoked it. But the above could be, perhaps poorly, argued to be strictly related to something that has been revoked; namely the ceremonies or the Levitical priesthood.
Question: On what basis can we appeal to the OT to justify doctrine and practice that does not directly relate to God's character or the gospel? E.g. in the realm of worship and ecclessiology.