When did the new covenant start?
- When Jesus died, not when Jesus was born.
"For a covenant is valid only when men are dead, for it is never in force while the one who made it lives." - Hebrews 9:17
So what covenant was still in effect while Jesus was alive teaching and preaching?- The old covenant
Does that mean we lump everything Jesus said and did into an "old" category that doesn't touch the new?- No, we don't throw the baby out with the bathwater. Neither do we administer certain medicine for one person's sickness to another without that sickness.
Jesus was the master physician and knew the entire purpose of the law was to break anyone of their self-righteousness so that they would cry out for a savior - it was the schoolmaster that pointed us to our need for Christ. (Gal 3:24)
So you see Jesus doing 2 things during his ministry:
1) Raising the standard of an already unkeepable law (613 commandments) to the very thoughts & intents of hearts. Pharisees thought if they never murdered, they were righteous, Jesus raises it and says if you are angry, you're a murderer. If you lust, you're an adulterer. You're only forgiven if you forgive. If your right hand causes you to sin, cut it off (this one gets washed over as hyperbole and exaggeration.)
What is he doing? Bringing the law back to its pristine standard and purpose - the intention of God was never that men keep the law - it was to break anyone of their ability to trust themselves - it was perfect medicine for the self-righteous heart so that the new covenant of grace would be received with humility, not with entitlement.
2) Ministering grace, love, unconditional forgiveness & acceptance to those who were already humbled, & broken. The woman caught in the act of adultery - by standards of the law was to be stoned, but Mr. Grace (Jesus) showed her grace & chased away every condemning voice against her. It was in this pure environment of no condemnation (no law but grace) she was empowered to go and sin no more.
The stories continue with lepers, tax collectors, cheats, the low caste of society - he had a much different message for them - the lost coin, the lost sheep, the prodigal son, than he did for the self righteous.
Was Jesus mixing covenants?- No, he preached law to those whom it was made for - the self-righteous, and prophesied of the grace that was to come after his death for those who were already broken. God in Christ was resisting the proud (law), and giving grace to the humble. (James 4:6) , What he taught his disciples was notably different than what he spoke against Pharisees. That comforts me.
Concerning responsibility for sin - if we are conditionally forgiven based on our forgiveness of others - I find it funny that Paul never once mentions it. Yet there are a whole slew of scriptures that attest to all of our sins being laid upon Christ - past present and future, and all sin being forgiven by God in Christ. My present position is that God has imputed all of my sin upon Christ with all of sin's punishment, wrath etc.. and IF I do sin, then my job is to get my eyes back on Jesus, not focus on my sin. Holy Spirit convicts me of righteousness, not sin. God has promised me under the main clause of the new covenant:
"For I will be merciful to their unrighteousness, and their sins and their iniquities will I remember no more." - Hebrews 8:12
The hot point of this statement makes people assume one is giving license to sin & they can just go do whatever they want if you tell people all of their sins are forgiven (even future sins)
*If that is all that you preach - unconditional forgiveness - that Jesus died for you (took all of your sin) and you DON'T preach the other half - that Jesus died as you (your old sinful self is dead and the new you is resurrected in Christ with a new clean, sinless nature) - then yes, you are setting people up to fall into licentiousness.
The message of finished works is 2-fold:
1) Jesus died for you (took all of your sin, sickness, poverty, shame etc..) so you could have all of his good
2) Jesus died as you (included you in his death, burial and resurrection to kill the old man and resurrect you into new life with a new heart and a new spirit - his law already written on your heart.)
Without both sides of this message - the grace covenant will continue to get discredited by preaching the incomplete gospel and creating grace hippies that don't know they have a new set of desires conducive with their new nature. Or we create people who know their old life is dead - but still relate to God on a performance-based relationship instead of grace-based where we "earn" (for lack of a better word) blessing from him rather than receive freely, and steward well in thanksgiving.
I'm so sorry this is so long. For sake of explanation on some of the above stuff I included a link to notes I made of a word I taught with a lot more scriptural references concerning law & grace, distinguishing covenants, and our role in them if anyone is interested.