It’s a form of praying with our senses…using our senses to remind us of God.
In the same way that you can use tedious or hard work to remind us God, perhaps asking for His help as we work, etc.
It comes from the Old Testament as you say.
But I think the idea is really to “offer God” what is good…incense…while letting the resultant smell take our mind to God. Smelling thus also becomes a means to draw closer to God.
Prayer is after all a movement to unity with God.
Fasting is a means of unifying ourselves with God, letting our hunger pangs remind us of Him.