And what is the connection between this security — this promised perseverance — and the cross of our Lord Jesus? Just before Jesus shed his blood for sinners, he lifted up the cup at the last supper and said in Luke 22:20, “This cup that is poured out for you is the new covenant in my blood.” What that means is that the new covenant, promised most explicitly in Jeremiah 31 and 32, was secured and sealed by the blood of Jesus. The new covenant comes true because Jesus died to establish it.
And what does the new covenant secure for all who belong to Christ? Perseverance in faith to the end. Listen to Jeremiah 32:40, “I will make with them an everlasting covenant, that I will not turn away from doing good to them. And I will put the fear of me in their hearts, that they may not turn from me.” The everlasting covenant — the new covenant — includes the unbreakable promise: “I will put the fear of me in their hearts, that they may not turn from me.” They may not. They will not. Christ sealed this covenant with his blood. He purchased your perseverance
If you are persevering in faith today, you owe it to the blood of Jesus. The Holy Spirit, who is working in you to preserve your faith, honors the purchase of Jesus. God the Spirit works in us what God the Son obtained for us. The Father planned it. Jesus bought it. The Spirit applies it — all of them infallibly. God is totally committed to the eternal security of his blood-bought children.