A wonderful comment from John Calvin on the freedom which Christians have to worship God without fear,
That we may serve him without fear This deserves our attention: for it implies that we cannot worship God in a proper manner without composure of mind. Those who are ill at ease, who have an inward struggle, whether God is favorable or hostile to them, whether he accepts or rejects their services,--in a word, who fluctuate in uncertainty between hope and fear, will sometimes labor anxiously in the worship of God, but never will sincerely or honestly obey him. Alarm and dread make them turn from him with horror; and so, if it were possible, they would desire that there were, "no God," (Psalm 14:1.) But we know, that no sacrifice is acceptable to God, which is not offered willingly, and with a cheerful heart.
Before men can truly worship God, they must obtain peace of conscience, as David speaks, "There is forgiveness with thee, that thou mayest be feared," (Psalm 130:4:) for those to whom God has given peace are graciously invited and led to approach him willingly and with a cheerful desire to worship him. Hence too Paul deduces that maxim, that "whatsoever is undertaken without faith is sin," (Romans 14:23.) But since God reconciles men to himself in Christ, since by his protection he keeps them safe from all fear, since he has committed their salvation to his own hand and guardianship, we are justly declared by Zacharias to be delivered by his grace from fear.
From his Commentaries on Lk 1:74.