The Lord is my helper; I will not fear. What can man do to me?

Hebrews 5-6
Let your conduct be without covetousness; be content with such things as you have. For He Himself has said, “I will never leave you nor forsake you.”[a] 6 So we may boldly say:
“The Lord is my helper; I will not fear. What can man do to me?”

Having taken the promise that God will never leave us or forsake us, then we have to respond according to our belief in that promise. We know God is true in His Word, and if we truly believe in God, then this promise should motivate us into boldness. Peter and the other apostles were bold after Pentecost, in preaching about the Kingdom of God. With the Holy Spirit in us, we too can act with this boldness. Fear will put thoughts into us, but it can be overcome by remembering this promise and that the Lord is my Helper.

I will never leave you nor forsake you

Hebrews 13:5
Let your conduct be without covetousness; be content with such things as you have. For He Himself has said, “I will never leave you nor forsake you."

This assurance of God is truly wonderful, if only we can grasp the entirety of it. There is no conditions mentioned here; it just says God will not leave nor forsake us. God knows our shortcomings, that we will continue to sin, that we can never be perfect as His Son Yshua, yet we have the guarantee that He will never leave us. Our respond can be none other than total devotion to Him.