^a ει τις θελει οπισω μου ελθειν... there are 2 aorist imperatives (απαρνησασθω and αρατω) and one present active imperative (ακολουθειτω). The distinction between aorist imperative and present imperative is ASPECT not tense, the expectation of the command is that the aorist tasks will be completed in full whereas the present imperative is an ongoing command. The cross must be picked up and the self must be denied if someone wants to be following Jesus.