John 13:17

If ye know (ei oidate). Condition of first class assumed as true, ei and present (oidate used as present) active indicative. If ye do (ean poihte). Third-class condition, ean and present active subjunctive, assumed as possible, "if ye keep on doing." Both conditions with the one conclusion coming in between, "happy are ye." Just knowing does not bring happiness nor just occasional doing.