Rashi quotes two rabbinic explanations – one, from the Sifre, that the priest had to stand on a step or platform in front of the menorah in order to kindle the lights; the second, from the Sifra on Lev. 24:2 and the Talmud Shabbat 21a, that because flames rise upwards, the lights had to be kindled well enough to allow the light to take hold and rise by itself.
The second explanation suggests a further question. Why do flames rise? There is a scientific answer, but there is also a spiritual explanation.
Light has a Divinely-allocated task. It has to be “a flame of God” (the phrase is from Shir haShirim 8:6, the only time God is mentioned in the Song of Songs). It has to be a flame that, as Rav Kook would say, like everything else in nature, constantly seeks to rise to God.
But flames are kindled by human beings, and human beings must ensure that the flames they light serve Divine purposes and are not, God forbid, used to harm other people, the environment or civilisation.