Watch should be translated here as in verse 38.

The that of pray that you may not enter into temptation can be interpreted to mean “Ask God to make sure you are not tempted (or, tested),” but it is also possible to understand “Pray to God, and then you won’t be tempted.”

Enter into temptation recalls the third petition of the Lord’s Prayer: “And lead us not into temptation” (6.13). Different verbs are used in the two passages (“lead” versus “enter”), but into temptation occurs in both, and it seems a valid conclusion that they mean the same. Translations vary between (1) the more general meaning of enter or fall into temptation (Revised Standard Version, New International Version, Moffatt) and (2) the more specific meaning of being put to the test or of undergoing a trial (New Jerusalem Bible, New English Bible, New American Bible, An American Translation, Die Bibel im heutigen Deutsch; Phillips “face temptation”). See further at 6.13.

The spirit indeed is willing, but the flesh is weak (so also Good News Translation, Jerusalem Bible, New English Bible) is a literal and meaningless rendering of the Greek text. A literal translation may tend to suggest a contrast between “spirit” and “flesh” in the Pauline sense, which is not at all the meaning in the context. The distinction is rather “between man’s physical weakness and the noble desires of his will,” as one commentator states it. Die Bibel im heutigen Deutsch translates “You have good intentions, but you are only weak human beings.” Barclay (“I know that you mean well and that you want to do the right thing, but human nature is frail”) and Phillips (“Your spirit is willing, but human nature is weak”) are similar.

Quoted with permission from Newman, Barclay M. and Stine, Philip C. A Handbook on the Gospel of Matthew. (UBS Handbook Series). New York: UBS, 1988. For this and other handbooks for translators see here .