If we give in to fear, we think thoughts which are not of God. This has many bad effects because "a thought" is the source "of every act" and "the root of all conduct is the mind" (Sir 37:16-17).
If we give in to fear, we think of ourselves as slaves (Gn 50:18-19). However, Jesus freed "those who through fear of death had been slaves their whole life long" (Heb 2:15).
If we give in to fear, we are intimidated, that is, manipulated (Mt 10:26). Fear is often used to silence us about the Lord (Mt 10:27).
We "have no fear" (Gn 50:21) when we believe that God our Father will provide for us (see Gn 50:21) by working together all things — even bad things — for our benefit (Rm 8:28; Gn 50:20).
We "do not fear" when we believe that no one can destroy our souls except God (Mt 10:28), Who does so only if we insist on not trusting Him and living for Him.
We "have no fear" when we believe that God the Father knows and loves us personally, individually, and tenderly (see Mt 10:29-31).
"Therefore have no fear" (Gn 50:21).