Then [Jesus] returned to the three disciples and found them asleep; and he said to Peter, “How is it that you three were not able to keep watch with me even for one hour? Keep watch and pray that you will not fall into temptation. The spirit is willing, but the flesh is weak.”

(Matthew 26.40-41 GNB)

Jesus did not say "the spirit is willing, but the flesh is weak" to excuse the disciples from failing to keep watch. It was not an excuse then and it is not an excuse now.

“God is Spirit, and only by the power of his Spirit can people worship him as he really is.”

(John 4.24 GNB)

The flesh has its battles, different from the spirit. But if the spirit is lost, then the flesh is surely lost. I must strengthen my spirit at all times and keep it right with God.

“Do not worship any other god, because I, the LORD, tolerate no rivals.”

(Exodus 34.14 GNB)

See: Jealous for me