There are a number of times in John's Gospel where it is a question of catching, getting ahold of, clutching, grasping, understanding, etc.; this is not a matter of vocabulary but of a certain motion which can be either physical, mental, or spiritual.  Here we see that especially in the last line of today's Gospel reading, where “they tried to seize Him,” a movement obviously physical and negative.  The alternate response to what Jesus offers here is parallel in a positive mental and/or spiritual attempt to get a grasp on what Jesus is saying, to comprehend His words.

We ourselves need to have some grasp of Jesus (spiritually and mentally), to maybe cling to Him (spiritually) at times in desperation and hope and maybe, at best, in love and still in hope.  There are many forms and shades of that, and each of us does it in a very personal way but always at least partly in the wrong way because we remain fallible, finite humans: we think we have a claim on God or presume that we grasp Him and all that He means and offers us, and we believe that our hold on God is strong enough to make Him remain there, limited to that single insight or encounter.  Jesus is always moving on, however, always calling us further and deeper in our knowledge of Him, in our trust in Him, and in our attachment to Him but also always in new ways that we don't need to fully understand in order for us to respond to them. 

In all of this we must believe that this action works in both directions: Jesus Himself has an absolutely strong and absolutely loving grasp on us.  He holds us in safety, in warmth, and for our good --- if only we will trust Him.  We need to base our lives on that and to give Him constant gratitude and thanks, finding everything about ourselves in Him first, last, and in all ways.