Markus 13:33

13:33 Watch out! Stay alert! ¹  For you do not know when the time will come.

Lukas 21:36

21:36 But stay alert at all times, ²  praying that you may have strength to escape all these things that must ³  happen, and to stand before the Son of Man.”

[13:33]  ¹ tc The vast majority of witnesses (א A C L W Θ Ψ Ë^1,13 Ï lat sy co) have καὶ προσεύχεσθε after ἀγρυπνεῖτε (agrupneite kai proseucesqe, “stay alert and pray”). This may be a motivated reading, influenced by the similar command in Mark 14:38 where προσεύχεσθε is solidly attested, and more generally from the parallel in Luke 21:36 (though δέομαι [deomai, “ask”] is used there). As B. M. Metzger notes, it is a predictable variant that scribes would have been likely to produce independently of each other (TCGNT 95). The words are not found in B D 2427 a c {d} k. Although the external evidence for the shorter reading is slender, it probably better accounts for the longer reading than vice versa.

[21:36]  ² sn The call to be alert at all times is a call to remain faithful in looking for the Lord’s return.

[21:36]  ³ tn For the translation of μέλλω (mellw) as “must,” see L&N 71.36.