From Latin 'diligere' (to choose apart) — careful choosing. 'Negligent' is its perfect opposite: 'not choosing, not caring.'
Careful and persistent work or effort.
From Old French 'diligence,' from Latin 'dīligentia' (attentiveness, careful exactness, love of one's work), from the adjective 'dīligēns' (careful, attentive), the present participle of 'dīligere' (to value highly, to esteem, to set apart as worthy of attention), composed of 'dis-' (apart, asunder — intensifying) + 'legere' (to choose, to pick out, to gather, to read), from PIE *leǵ- (to gather, to collect, to speak). Dīligere literally means 'to choose-apart' — to single something out as deserving your full attention and love. Diligence is the sustained
'Diligence,' 'intelligence,' 'lecture,' 'lesson,' 'legend,' and 'elect' all come from Latin 'legere' (to choose/read/gather). Diligence is choosing-apart (careful selection). Intelligence is choosing-between (discernment). A lecture is a reading. A lesson is a reading assignment