When you roll Initiative, you can cast Haste on yourself without taking Radiant damage or expending a spell use. When you cast the spell, it doesn't require Concentration and, when the spell ends, you don't have the Incapacitated condition and your Speed isn't 0.
Once you use this feature, you can't use it again until you finish a Long Rest. You can also restore your use of it by taking 30 Radiant damage (no action required). This damage ignores Resistance and Immunity, and bypasses Temporary Hit Points.