There is an easy parallel between Isaac bound in the first reading and the paralytic being carried in the gospel reading. In both cases God saves the bound one, in the case of the gospel God acts in Jesus. It is easy to place ourselves in these stories. We might see ourselves as the one tied down, the paralysed one, the one in need of God's help if we are to break free and get moving again. Or we may see ourselves as people who carry others to Christ for his healing, anybody we are involved in caring for, teaching, helping, strengthening.
There is, as always, another level of meaning, the Christological one. Jesus will become the paralysed one, the one tied down, in order to achieve the world's salvation through his love and obedience. There are clear hints of this Christological reading in how we must inevitably now hear the story of the sacrifice of Isaac. 'Where is the lamb for the sacrifice', the lad asks. We know the answer to that. Isaac carried the wood for the sacrifice, a detail to which John's gospel makes clear allusion when it tells us that Jesus himself carried the cross on which he was to be crucified.
But the strongest hint is in the fact that both Isaac and Jesus are only sons. The sacrifice of Isaac is made even more poignant by the fact that it is Abraham's only son, whom he loves, who is to be slain. The sacrifice of Jesus is the sacrifice of the Only Son of the Father. Isaac is the only son of the promise, Jesus the only son who, his disciples hoped, would set Israel free.
That someone is an only child or an only son is normally only mentioned in the Bible when it is a question of their death. The mourning for an only child is greater than any other kind of mourning (Zechariah). The dismay of Jephthah is all the greater because the daughter he sacrificed was his only child (Judges). God, who spared the (only) son of Abraham, did not spare His own (only) Son but gave him up for us all (Romans 8).
It became part of Jewish belief that the Messiah was 'earned' for Israel by Abraham in this moment in which his faith was radically tested. He was ready to trust God even in this moment in which God seemed to contradict Himself. The coming of the Messiah was regarded as a reward for the faith Abraham showed in being prepared even to sacrifice his only son, Isaac.
It set the stage for an even more mysterious sacrifice. Which is easier, to say 'your sins are forgiven' or to say 'arise and walk'. It seems the first is easier because how can people know whether anything has happened or not? But in another way the second is easier, to heal a physical ailment than to effect the forgiveness of sins. The sacrifice of the Only Son is the price paid for the forgiveness of our sins. We can enter more deeply into this mystery by either door, coming to appreciate better the power and resistance of sin, or coming to appreciate better the love and obedience of Jesus. This is the fulfilment of God's promise to Abraham, the way in which all the nations have been blessed by this son of Abraham.