Ephesians 6:18 & Jude 1:20 - Pray in the Spirit.

Eph.6:18 & Jude 1:20: Pray in the Spirit.

Eph 6:18 (NEB)  Give yourselves wholly to prayer and entreaty; 
pray on every occasion in the power of the Spirit. To this end keep 
watch and persevere, always interceding for all God's people;  

Jude 1:20 (NLT)  But you, dear friends, must continue to build 
your lives on the foundation of your holy faith. And continue to pray 
as you are directed by the Holy Spirit. 

We are to live or walk 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. 

We are to do all things by His Spirit:
Zec 4:6b (KJV) Not by might, nor by power, but by my spirit, 
saith the LORD of hosts. 

So why shouldn't we be expected to pray in the Spirit:

Well just how do we pray in the Spirit:

It is praying while guided by the Spirit of God: [Ryrie SB]

It is praying as the Spirit leads.  [Wiersbe Expository Outlines]

It is to pray in the power and strength of the Holy Spirit. 
[Life Application SB] 

It is to pray according to the Spirit's promptings and with the 
power of the Spirit. [NIV SB] 

It is to pray in accordance with the Holy Spirit's directives 
and with the Spirit's aid. [SDA Com] 

It is to pray under his guidance and influence, according to the 
rule of his word, with faith, fervency, and earnestness; this is 
praying in the Holy Ghost. [Matthew Henry Commentary] 

It is to submit our hearts and minds to the direction and 
leading of the Holy Spirit and then pray in his power. [Quest SB] 

It is holding fast the divine influence which ye have received, 
and under that influence making prayer and supplication to God. 
(Adam Clarke Commentary) 

Mark the grand characteristic of true prayer--"In the Holy 
Spirit." The seed of acceptable devotion must come from heaven's 
storehouse. Only the prayer which comes from God can go to God. We must 
shoot the Lord's arrows back to him. That desire which he writes upon 
our heart will move his heart and bring down a blessing, but the 
desires of the flesh have no power with him.  
Praying in the Holy Spirit is praying in fervency. Cold prayers 
ask the Lord not to hear them. Those who do not plead with fervency, 
plead not at all....  
It is praying perseveringly. As one prays he gathers force as he 
proceeds, and grows more fervent when God delays to answer. The longer the 
gate is closed, the more vehemently does he use the knocker, and the 
longer the angel lingers the more resolved is he that he will never let 
him go without the blessing. Beautiful in God's sight is tearful, 
agonizing, unconquerable supplication.  
It means praying humbly, for the Holy Spirit never puffs us up 
with pride. It is his office to convince of sin, and so to bow us 
down in contrition and brokenness of spirit. We shall never sing 
Gloria in excelsis except we pray to God De profundis: out of the 
depths must we cry, or we shall never behold glory in the highest.  
It is loving prayer. Prayer should be perfumed with love, 
saturated with love--love to our fellow saints, and love to Christ.  
Moreover, it must be a prayer full of faith. A man prevails only 
as he believes. The Holy Spirit is the author of faith, and 
strengthens it, so that we pray believing God's promise.  
O that this blessed combination of excellent graces, priceless 
and sweet as the spices of the merchant, might be fragrant within us 
because the Holy Spirit is in our hearts! Most blessed Comforter, exert 
thy mighty power within us, helping our infirmities in prayer.  
Morning and Evening by Charles H. Spurgeon