You cannot enter that grace unless you have living faith, faith with obedience, faith with repenting of those sins Jesus died for.
Logically, start at the historical fact, that is undisputed: Five men were given the death penalty for witnessing to the raising of the Lord Jesus from the dead on the third day; Stephen, James the son of Zebedee brother of the Apostle John, Peter and Paul, and James the author of the eponymous epistle in the New Testament. These facts are recorded within the generation that they happened, the stoning of Stephen and execution of James the brother of John in Acts, the execution of James the non-Apostle/bishop in Josephus, and the executions of Peter and Paul in Rome in Clement's epistle to the Corinthian diocese (with less-firm evidence, it's nonetheless reasonable to accept that all Twelve of the Apostles were also, as Church tradition testifies, given the death penalty for their own witness to the resurrection of Jesus Christ from the dead on the third day; and besides the fact of these executions, there is the also important fact that there is zero evidence of any Apostles or first bishops of the Church, ever recanting and saying it was made up---zero).
This means it happened. Paul himself says that believing in the resurrection of the Lord Jesus from the dead on the third day, along with confessing with the mouth that Jesus Christ is Lord, is all that's needed for grace through faith, Romans 10:9 (KJV).
The whole rest of Christian theology is explaining all that the resurrection of the Lord Jesus Christ from the dead on the third day means, all that it confirms and proves, as logically necessary further facts. They work both back into the past that led up to the resurrection, and they work forward into the future. The Apostles and writers of the New Testament made it their mission to first and foremost distribute the good news of (verbally; orally and written), and the formal remembrance of, the resurrection of the Lord Jesus from the dead on the third day (the Eucharist), and then to explain all that the resurrection therefore proves and confirms, both in the past leading up to the resurrection, and into the future concerning what we know must also now come to pass.
But the mustard seed of faith, is in the Lord Jesus rising up from the dead on the third day.