The shadow of death could be referring to the death of our hopes and dreams or our job security or even our relationships. The shadows we fear the most are the death of our loved ones or the loss of our health.
God has promised us that He will never leave us or forsake us. He sent His Son so that we would have someone with us for the journey through those shadows. We have the Holy Spirit to be our comforter and our guide as we travel the road through that valley.
I noticed that the verse says we would 'walk' through the valley. To me, that seems to be a progression through the
valley. We will walk through denial, anger, bargaining, and
finally to acceptance if we allow the Spirit to walk with us.
Isaiah 42:16 promises that God will guide us through and will turn the darkness into light. He will make the rough places smooth. He promises He will not forsake us. His word is truth and a promise that cannot be broken. He may lead us
down paths of pain and confusion for us, but He knows the
beginning from the end and His plan for us was written before the beginning of time.
There is an end to the valley and the shadows will disappear. We will walk with Him in the Eternal City and there will be no more tears. No more losses that break our hearts and there will be no more shadows to cause us to fear.
While the path that we must walk is not an easy one, He has promised to give us the treasures of darkness. Isaiah 45:3. Those treasures are sometimes hard won but the Lord honors us with His love and patience. He will walk every step of the way with us and never leave us alone in our fears.