Passage
so shall my word be that goeth forth out of my mouth: it shall not return unto me void, but it shall do that which I please, and it shall accomplish that for which I send it.
so shall my word be that goeth forth out of my mouth: it shall not return unto me void, but it shall do that which I please, and it shall accomplish that for which I send it.
Isaiah 55:9 For [as] the heavens are higher than the earth, so are my ways higher than your ways, and my thoughts than your thoughts.
Isaiah 55:10 For as the rain cometh down, and the snow from heaven, and returneth not thither, but watereth the earth, and maketh it bring forth and bud, that it may give seed to the sower, and bread to the eater:
Isaiah 55:11 so shall my word be that goeth forth out of my mouth: it shall not return unto me void, but it shall do that which I please, and it shall accomplish that for which I send it.
Isaiah 55:12 For ye shall go out with joy, and be led forth with peace; the mountains and the hills shall break forth before you into singing, and all the trees of the field shall clap their hands.
Isaiah 55:13 Instead of the thorn shall come up the cypress, and instead of the nettle shall come up the myrtle; and it shall be to Jehovah for a name, for an everlasting sign [that] shall not be cut off.
The verse centers on "return unto me", "shall", "word", "goeth", "forth", "mouth", and "void". It is saying that the verse draws attention to "return unto me" and "shall", so its meaning should be read from those terms before moving to application.
The nearby context moves from verse 10's "For as the rain cometh down and..." into verse 12's "For ye shall go out with joy...", so "return unto me" and "shall" belong inside that flow. In Isaiah context, the local focus is the Holy One of Israel, judgment and restoration, the servant of the LORD, and Zion's hope.
A plain takeaway is to answer the verse's own emphasis on "return unto me" and "shall" with trust shaped by these words, not by a vague optimism outside the passage.