If I will (εαν θελω). Condition of the third class with εαν and the present active subjunctive of θελω.

Till I come (εως ερχομα). Literally, "while I am coming" (εως and the present indicative, not εως ελθω (second aorist active subjunctive).

What is that to thee? (τ προς σε;). A sharp rebuke to Peter's keen curiosity.

Follow thou me (συ μο ακολουθε). "Do thou me keep on following." That lesson Peter needed.