I believe you completely misunderstand how God related to the people in the old testament. There is no change in God between the testaments. It is an eternal principle always the same that it is only grace that gives salvation. Obedience has never, ever produced grace from the Lord. If anyone was under the law for grace they would have to be perfect and man has never been perfect. In the old testament they were under grace not law for salvation. That grace came with repentance and blood given on the altar, symbolized by the blood of animals.
If you post is to tell us that obedience was necessary for salvation in the old testament you are misrepresenting our holy eternal God.
You're mixing OT and NT concepts of grace. Grace is what is bestowed upon people by God without they're deserving it, largely when they are acting to please God. OT grace brought forgiveness, but not salvation. NT grace brought salvation.
OT grace did *not* bring salvation, since salvation only comes after Christ produced redemption at the cross. To say that grace brought salvation before Christ did this, while still in the OT era, is in error, and diminishes the necessity of Christian redemption.
Grace was indeed active under the Law, if you define "grace" according to the Bible. It is another word for God's "kindness." God's kindness indeed extended, temporarily, through the Law. That was the whole reason that animal sacrifices were provided for, to bring a measure of forgiveness to Israel when they failed. They didn't deserve mercy, but God offered it anyway. And even when Israel failed the entire Law, God provided mercy to restore Israel after their captivities.
I don't know what you mean by saying people under the Law had to be perfect to experience God's love and kindness? David sinned with Bathsheba, and still obtained kindness from the Lord. Solomon failed in some ways, and yet God's kindness was never fully taken from him. He retained the Southern Kingdom of Judah. These men did not need to be perfect to obtain grace, or kindness, or forgiveness.
You seem only to be talking about the need of perfection to obtain a place in heaven, which is salvation. In NT terms, we find our place in heaven, or salvation, through Christ's perfection, and not through our own. We obtain grace from Christ, which is salvation. This is only in the NT era.
I don't know what you mean that OT saints were under grace, not Law, for salvation? There was *no* salvation in the OT era. They only had the hope and the faith necessary to obtain salvation *after* Christ's redemption at the cross. They certainly were under the Law and experienced a measure of grace under the Law. But they did not experience Christian salvation!
Their faith made them eligible for Christian salvation, but did not experience salvation until after Christ came and died for their sins. All redemption under the Law was temporary, awaiting final validation at the cross. I believe your words are not being used correctly, leading to misleading statements.