As David notes, God's angel is present with those who fear Him, and He delivers them. In this context, the word translated as "fear" implies deep respect and reverence, not fear. David is giving his personal testimony in this statement. Today, Jesus is always with us, and no matter what difficulty we encounter, He will never leave us. 
Angels are God's servants who provide a variety of services to us. After the incarnation of Christ, the Angel of the Lord does not appear in the New Testament, and as born-again believers, we are not in need of a visitation by the Angel of the Lord because Jesus Christ was born into the world and His Holy Spirit dwells within us, as our guardian and guide.
Christ also promises that He will never leave nor forsake any of us. It is His assurance that nothing can pluck us from His hand or our Father's hand. Our psalmist rejoiced that the Angel of the Lord encamped round about those who fear Him, and we can also rejoice with exceeding great joy that the Spirit of Christ has taken up permanent residence within our hearts.

Dear Heavenly Father, the knowledge that You are with me at all times and anywhere is comforting and reassuring. Thank You for allowing me to rejoice in my sufferings with exceeding joy as a partaker of Christ's sufferings, knowing that at the reveal of Christ's glory, I will know Him as He has known me. Throughout the day, I feel Your goodness, mercy, protection, and grace surrounding me, and I pray You will send Your messengers of comfort to protect me from the influence of darkness. 
In Jesus's name I pray. Amen.