49 Heb “listen”; “obedient”; “If you consent and obey.”
50 The wordplay in the Hebrew draws attention to the options. The people can obey, in which case they will “eat” v. 19 (תֹּאכֵלוּ [to’khelu], Qal active participle of אָכַל) God’s blessing, or they can disobey, in which case they will be devoured (Heb “eaten,” תְּאֻכְּלוּ, [té’ukkélu], Qal passive/Pual of אָכַל) by God’s judgment.
51 Heb “for the mouth of the Lord has spoken.” The introductory כִּי (ki) may be asseverative (as reflected in the translation) or causal/explanatory, explaining why the option chosen by the people will become reality (it is guaranteed by the divine word).

In other versions

If you are willing and obedient,

you shall eat the good of the land;

but if you refuse and rebel,

you shall be eaten by the sword;

for the mouth of the Lord has spoken.”

If you are willing and obedient,

you will eat the good things of the land;

but if you resist and rebel,

you will be devoured by the sword.”

For the mouth of the Lord has spoken.

If you are willing and obedient,

you will eat the good things of the land.

But if you refuse and rebel,

you will be devoured by the sword.”

For the mouth of the Lord has spoken.

If you will only obey me,

you will have plenty to eat.

But if you turn away and refuse to listen,

you will be devoured by the sword of your enemies.

I, the Lord, have spoken!”

If you are willing and you are obedient,

you shall eat the good of the land.

But if you refuse and you rebel, you shall be devoured by the sword.

For the mouth of Yahweh has spoken.”

If ye be willing and obedient, ye shall eat the good of the land:

But if ye refuse and rebel,

Ye shall be devoured with the sword:

For the mouth of the Lord hath spoken it.

Public Domain