Preaching is a balancing act. You are always in danger of overemphasizing some element in a text so that you misrepresent the whole. For example:
1. A theologically weighty word can send you up like a rocket. For example, I was working with a group of preachers looking at Ephesians 1:3-14. We observed features of the text, including the references to God and the relationships within the Trinity, we saw the amount of grace, love, lavished, blessing language. We saw all that God has done for us, in Him. But then we saw the word that might light the fuse and obliterate everything else – predestined! It would be so easy to take off and end up with a message bereft of intra-trinitarian relationality, stone cold and lacking in loving grace toward us, with some personal hobby horse message on predestination (in favour or against, depending on your position). Of course one should preach about predestination in the course of preaching this passage, but not to the exclusion of all else that is so richly interwoven!
2. A seemingly misplaced verse can take over the passage. For example, we were looking at Ephesians 2:1-10. Verse 10 is intriguing. Should it be seen as part of what Paul is saying in 8-9, or does it stand alone? Various groups processed the passage in different ways. Those that included 10 with 8-9 seemed to recognize it as a sub-point (i.e. after affirming that we are not saved by works, Paul does cover himself in case any miss his point and neglect good works altogether, but the focus is on God’s saving grace). Those that separated out verse 10 seemed to end up seeing the whole passage as culminating in the good works of believers, the goal of all that God did in our salvation. In one approach the verse was a passing, albeit important sub-point. In the other approach, it became the goal of all. I’m not affirming one or either of these here, I’m just making the point that how we see a verse working with those around it will determine our understanding and explanation of the whole.
3. A vivid image in a text can overwhelm the whole. So there’s a term in your passage that is particularly vivid and preaches so well in terms of visual imagery. Be careful that it doesn’t take over the message and end up becoming the dominant motif for the whole passage, when in reality it is a small part of a much bigger whole.
Understanding a passage is so much more than simply checking what words mean in a biblical dictionary and breaking the passage down into sections. The whole issue of relative weight and flow of thought is a massively important element in studying a biblical passage.