Mat 26:41: Watch and pray, that ye enter not into temptation: the spirit indeed is willing, but the flesh is weak.
In St. Luke's account of the incident where this Scripture occurs we read that when Jesus saw them sleeping, He said unto them
“... Why sleep ye? rise and pray, lest ye enter into temptation.” Luk 22:46
Comparing this with what’s recorded in St. Matthew and Mark's Gospels, it means Jesus was simply saying
“stay/keep awake and pray, that ye enter not into temptation: the spirit indeed is willing but the flesh is weak.”
In other words, the Lord Jesus was simply admonishing His disciples not to slack off or be lazy but to be prayerful.
From this portion of Scripture, we understand that prayer or being prayerful is how we keep ourselves vigilant and diligent as saints, it is how we keep ourselves from entering into temptation; it is what enables us to give expression to the desires of our recreated human spirits.
It is also how we walk in the Spirit for by so doing (consistently praying/being prayerful) we keep ourselves from giving into the weaknesses of the flesh and entering into temptation, that is, from fulfilling the lusts of the flesh. This is comparable to what the Scripture says about walking in the Spirit.
*[[Gal 5:16]] KJV* This I say then, Walk in the Spirit, and ye shall not fulfil the lust of the flesh.
Again, in the place of praying in the Spirit, we are lending ourselves to the leadership of the Spirit for it is us praying from our spirits as the Spirit gives us utterance: cf. Acts 2:4; 1Cor.2:13, and we know from James 3:2 that where the tongue leads, the body follows, that is, our tongues or the words of our lips can be used to bridle the body.
Therefore, in conclusion, by praying consistently in the Spirit we are training our bodies to yield to the leadership of God's Spirit.