The word fear in the expression “fear of the Lord” means awe or profound respect. It does not mean literal fear of God’s power but an awe and respect for the absolute majesty of God. We should “fear” offending God not because of his just punishment but because he is all good and deserving of our love.
As Pope Francis has said:
[Fear of the Lord] does not mean being afraid of God: we know well that God is Father, that he loves us and wants our salvation, and he always forgives, always; thus, there is no reason to be scared of him! Fear of the Lord, instead, is the gift of the Holy Spirit through whom we are reminded of how small we are before God and of his love and that our good lies in humble, respectful and trusting self-abandonment into his hands. This is fear of the Lord: abandonment in the goodness of our Father who loves us so much (General Audience, June 11, 2014).