Go not forth into the field, nor walk by the way; for the sword of the enemy and fear is on every side.
He addresses "the daughter of Zion" (Jeremiah 6:23); caution to the citizens of Jerusalem not to expose themselves to the enemy by going outside of the city walls.
Sword of the enemy - literally, there is a sword to the enemy; the enemy hath a sword.
Wallow thyself in ashes - (Micah 1:10, "Roll thyself in the dust"). As they usually in mourning only "cast ashes on the head," wallowing in them means something more-namely, so entirely to cover oneself with ashes as to be like one who had rolled in them (Ezekiel 27:30).
As for an only son - the most bitter lamentation that one can conceive. (Zechariah 12:10, "They shall mourn for Him (Messiah), as one mourneth for his only son, and shall be in bitterness for Him, as one that is in bitterness for his first-born").
Lamentation - literally, lamentation expressed by beating the breast х micpad (H4553)].