'Singleness' in the Bible

Day by day, continuing steadfastly with one accord in the temple, and breaking bread at home, they took their food with gladness and singleness of heart,

Servants, be obedient to those who according to the flesh are your masters, with fear and trembling, in singleness of your heart, as to Christ;

Servants, obey in all things those who are your masters according to the flesh, not just when they are looking, as men pleasers, but in singleness of heart, fearing God.