The Delta is that difference between the standard God has set for us in His LawWord and where we actually are in our current state of sanctification.
The standard God has set for our sanctification is not to be confused with our salvation which is already perfectly achieved and guaranteed to believers by the resurrection of Christ. The standard is God’s character: holiness, righteousness, knowledge, and dominion – in other words the communicable attributes of God – as set forth in His Law. We are to grow in each of these areas as long as we are alive.
Getting there from where we are is what I call Working the Delta.