Excerpt from the Tract:
Yet, the continuation of your relationship with your parent (or child depending on the perspective) is not based upon the quality or proficiency of the child’s obedience. No good parent ever removes his son from his house simply because the child disobeys. We expect a child to be incompetent, apathetic, unsure, and occasionally resistant to our instructions. In those moments our relationship to them is not interrupted.
When those childish actions arise, as parents we demand of the children a change in their actions. That discipline just mentioned comes into play. But while the children are learning the lessons that come to them only through the maturation of experience, we do not severe our ties to them because they have not yet amended their ways and apologized for their actions. We are long-suffering and patient with them because we understand that in time they will understand and grow into the people we know they can be.
So even in times when discipline is needed, the relationship between parent and child continues. It is sustained because the same blood flows through our veins that runs through theirs. We are bound to them because we gave them life. That bond would move us to give our lives for them if it would save theirs.
Is that not exactly what God has done for us? He is bound to us by blood. The blood of His Son covers us and continually cleanses us from sin.