"For as the rain and the snow come down from heaven and do not return there but water the earth, making it bring forth and sprout, giving seed to the sower and bread to the eater, so shall my word be that goes out from my mouth; it shall not return to me empty, but it shall accomplish that which I purpose, and shall succeed in the thing for which I sent it."Isaiah tells us something specific about the effect that the word of God has in the world. When God's word is introduced into the world though scripture, teaching or preaching it accomplishes something: unfailingly and purposefully. God doesn't waste his words.
What Isaiah hints at is that it may take some doing for God to get this done. In the metaphor of the rain to bread process there's sprouting and seeding, harvesting and baking. And finally bread is produced. God's word is no different. Don't assume that a single hearing of a pithy sermon or a Bible motto will produce the desired transformation God intends to effect in your life. The word has to take root, it has to grow, it has to be harvested and it has to be applied. God's word is powerful tool for radical life transformation, but not a tool for invasion. God's word goes where it is invited and it achieves what we allow it to.
What Isaiah doesn't tells us is that God will accomplish what He intends, but that may not be what we intend. God's word is intimately and unbreakably tied to God's will. Although we can choose to allow it to enter our lives, there is no predicting the level of transformation it will accomplish once we allow it. Remember, God's word accomplishes what God intends not what we desire.