Lissandra's kit main objetive in a game is to use her hard cc to lock down enemies and to use her ult and w to start a tf, also is very important to lissandra to keep herself alive so her passive will keep activating and dealing damage and slow to the enemy team.
But when lissandra is built with burst purposes she often decays late game since her kit and zhonya's are usually not enough to get into the enemy team, get a kill, and get out of there alive, only happening when she is extremely strong already. So, the main purpose of this build is to make lissandra more of a battle mage so she can slow the enemy team, hard cc enemy champions and proc her passive the most possible and deal a lot of damage overtime with liandry's.