In the sacrifice Abraham did lose Isaac. And that is the freedom. He did also get him back, though not in the physical way, for that would be a return to holding on, but he did receive back the true promise and essence of the gift of Isaac which he could never receive if he were to hold on to him bodily. What he gives up remains given up, i.e. henceforth he recognized Isaac as not belonging to him at all, but the true Isaac whom he holds on to by the strength of God’s promise in the face of the absurd is now given to him.