This passage occurs in the Narrative Lectionary, Year 1 (Most recently Sept 29, 2014).
For those on the NL: I struggle a great deal with this text, because the innocent seem to suffer. Perhaps, never really suffering oppression, I do not understand the harsh realities that undergird this text (escape from slavery and destruction of the military that allows for the system). Here the Word of the Lord teaches me that some systems are so horrifically out of line with God's intentions that they will be destroyed, not simply by human weapons, but by God.
If this is altogether too much, you can focus the fact that the Israelites are not so much told to be still, but to be quiet. Sometimes, we need to be very quiet to see God at work!
ילחם from לחם ("lakham", "fight", 14.4): The word here means fight; in the niphil form (which it is here), it means wage war. The "Lord Sabboth" (YHWH) is a God willing to fight for his people.
לכם("lakem"; two words, "to you all"; 14.4): God is not telling a particular individual to stay still, but the whole nation. He will fight for all the people, the good, the bad, the lame. In fact, he is speaking to the people that were just complaining. He will free all who were enslaved.
תחרישון from חרש ("hkarash"; "be silent"; 14.4) This word is translated here as "still" but it also means "be silent." I think the be silent is more relevant here because the Israelites have been complaining. Its not about "letting go" but "shutting up" ;-)
Here are some other uses of this verb:
Esther 4:14 For if you keep silence at such a time as this, relief and deliverance will rise for the Jews from another quarter, but you and your father's family will perish. Who knows? Perhaps you have come to royal dignity for just such a time as this."
Job 33:33 If not, listen to me; be silent, and I will teach you wisdom.
1 Samuel 7:8 The people of Israel said to Samuel, "Do not be silent in crying out to the LORD our God for us, and pray that he may save us from the hand of the Philistines."
רוח ("ruach", "spirit"/"wind"; 14:21)
When I first read vs 21, I was thinking a lot of Genesis 1: The Spirit moving; God dividing things; dry land appearing. As it turns out, none of the words really match up. Divide and dry land are different words than in Genesis 1. Spirit here really means east wind...but...but...it is worth pointing out that the Spirit must be sent to engage against the forces of chaos and death. I don't think one really stretches the Hebrew or theological narrative to say that the Exodus recalls, if not relives, the creation story of a God whose Spirit moves against chaos to create life.