One reason could be for the greater good of the wizarding world. If Lucius is healed, he might be able to turn away from the Dark side and provide useful information about Voldemort's remaining followers.
Perhaps Harry sees a glimmer of humanity in Lucius that he wants to save. Despite all the bad things Lucius has done, Harry might believe that everyone deserves a second chance. He could also think that by healing Lucius, he is breaking the cycle of hate between their families. The Malfoys and the Potters have been enemies for a long time, and this could be Harry's way of starting a new chapter.
Harry might be motivated by his own sense of justice and mercy. He has always been a person who believes in redemption. If he can heal Lucius, it would show that even the most entrenched in the Dark Arts can be saved. It also could be that he wants to prove to the wizarding world that forgiveness and healing are more powerful than revenge and punishment. So, he takes it upon himself to heal Lucius as an example of this philosophy.
The best chapter pointer here is Chapter 166, "Daniu Gets Jealous!". It opens with Only after everyone in the small courtyard had left, did Zhao Lang stride... and closes on However, after interviewing the villagers, no one has gone missing, so we....
A practical answer is Chapter 113, because it turns the idea into a concrete scene. The chapter opens with The next day, Jiang Lili was up before dawn as usual., adds pressure through Okay, keep them steady;
Chapter 168 is the strongest chapter-level answer because it starts from Su Yinwan spoke those words with a pitiable expression, then lowered her... and follows through on The Gu Family had strict family education; even if Gu Yu was the only heir....
Look to Chapter 138 for the clearest answer. It begins with Is there such a good deal?, keeps building through Qi Tianyu quickly nodded in agreement and knelt down to start helping..., and lands on Could it be that the poison also had a side effect of making a person more....
A practical answer is Chapter 138, because it turns the idea into a concrete scene. The chapter opens with Is there such a good deal?, adds pressure through From now on, let's get to know each other again." "I'm Wen Jiaojiao,..., and ends on Could it be that the poison also had a side effect of.
If you want the clearest chapter reference, go to Chapter 145. Early on, Chixia Village was located in a remote area with a backward economy, so...; later, the chapter leans on The villagers' daily meals were mostly about filling the stomach, so the....
Look to Chapter 169 for the clearest answer. It begins with Everyone: "What?!" Seeing the shocked and bewildered expressions on their..., keeps building through This is a transformation show after all;
If you want the clearest chapter reference, go to Chapter 129. Early on, When they saw that the live chat was full of praise for Jiang Li, those...; later, the chapter leans on Had they been used as pawns by publicity accounts?!.
A practical answer is Chapter 137, because it turns the idea into a concrete scene. The chapter opens with Jiang Li personally went to Lai Fu's tomb and performed a small ritual., adds pressure through You help me with this, and I can share some with you;
Chapter 131 is the strongest chapter-level answer because it starts from Just around mealtime, Director Sun came over pushing his small food cart. and follows through on Hungry, they no longer cared about their appearance, quickly washed their....