Roman Law
There is an interesting point in Roman law that I learned about some years back. Apparently, under Roman law, a parent could disown a child only if that child was biologically theirs. If the child was adopted, it was actually illegal to disown the child. This makes sense, if you think about it: you do not get to choose the children you give birth to; you do deliberately choose the children you adopt. Therefore, the choice ought to be binding. Thus, according to Roman law, if you adopt a child then, no matter what that child grows up to be, no matter what they do, they are yours.
There is significance in the fact that God “adopts” us as His children. We are not naturally born sons or daughters of God; we are creatures first. In being united to Jesus through the sacraments, we are adopted as sons and daughters of God. God makes a deliberate choice to make us His own; it is one that cannot be undone. We can still reject that love ourselves and rupture that relationship, but He will always take us back if and when we come back to Him. There is nothing that we can do to make God stop loving us.
No matter what sins we have committed, no matter how far we may stray, God will always welcome us back in confession. Jesus, as the Good Shepherd, will always come to seek us out when we are lost. May we have full confidence in that infinite and eternal love God has for each us, His adopted children!