Energy can neither be created nor destroyed, but it can change form. This means that within a closed system, the amount of energy at the beginning will equal the amount at the end, although the form(s) of the energy may be completely different. Energy at time T equals Energy at time T+1.
Work is measured in energy units of measure (e.g. joules, ergs, electron volts, etc..) because Work is a physical manifestation of energy. To better explain models and observed phenomena Work is therefore often semantically distinguished from other forms of energy within a system, but must always be treated as just another form of energy, e.g.