The operative word in Hebrews is better. The writer is contrasting the old covenant with the new and specifically focusing on how Christ is better than anything else we have from God. In Chapters 3 and 4 he is examining the concept of "rest". There is much that can be said in regard to this concept. It is a good study to look at how he approaches "rest" and how this concept relates to our position in Christ. I recommend the study but I am not going to go into detail about that now. What I would like you to focus on is that his comment on the piercing quality of the Word of God comes at the end of his thoughts on "rest".
It seems that our engagement in and with the Word of God is connected to our entering into this rest. Further, the writer expands this in chapter 5 by telling us that we need to continue to grow in our intake of the Word of God not settling for milk, but moving on toward meat.
Take a look at that sequence from 3 - 5 for yourself and come to your own conclusions. Mine are that our intentional engagement in the meat of the Word is critical to entering into the rest that God promises.