Rashi on Leviticus 24:7/רש"י על ויקרא כ״ד:ז׳

1ונתת על המערכת AND THOU SHALT PUT UPON THE ROW — i. e. upon each of the two rows [PURE FRANKINCENSE]; there were two bowls for this frankincense, each filled with a handful of it.

2והיתה THAT IT — this frankincense — MAY BE

3ללחם לאזכרה ON THE BREAD FOR A MEMORIAL — because of the bread itself nothing was offered to the Lord, but the frankincense was burnt when the former was removed from the golden table every Sabbath. It (the frankincense) thus served as a memorial for the bread, because through it, it (the bread) was recalled to memory Above (the bread itself was not offered) just as the “handful” of flour and of oil (Leviticus 2:2) was “the memorial portion” of the meal offering being the only part offered, while the remainder was eaten by the priests just as this bread was.