Then it will be, when many evils and troubles have found them, that this song will answer them as a witness (for it shall not be forgotten from the mouths of their seed); for I know their intent which they are developing today, before I have brought them into the land which I swore.”
Deuteronomy 31:19 “So now, write this song for yourselves and teach it to the sons of Israel; put it in their mouths, so that this song may be a witness for Me against the sons of Israel.
Deuteronomy 31:20 For when I bring them into the land flowing with milk and honey, which I swore to their fathers, and they have eaten and are satisfied and become fat, then they will turn to other gods and serve them and spurn Me and break My covenant.
Deuteronomy 31:21 Then it will be, when many evils and troubles have found them, that this song will answer them as a witness (for it shall not be forgotten from the mouths of their seed); for I know their intent which they are developing today, before I have brought them into the land which I swore.”
Deuteronomy 31:22 So Moses wrote this song the same day and taught it to the sons of Israel.
Deuteronomy 31:23 Then He commissioned Joshua the son of Nun and said, “Be strong and courageous, for you shall bring the sons of Israel into the land which I swore to them, and I will be with you.”
The verse centers on "evils", "troubles", "found", "song", "answer", "witness", "shall", and "forgotten". It is saying that the verse draws attention to "evils" and "troubles", so its meaning should be read from those terms before moving to application.
The nearby context moves from verse 20's "For when I bring them into the..." into verse 22's "So Moses wrote this song the same...", so "evils" and "troubles" belong inside that flow. In Deuteronomy context, the local focus is covenant, worship, and faithfulness.
A plain takeaway is to answer the verse's own emphasis on "evils" and "troubles" with trust shaped by these words, not by a vague optimism outside the passage.