Ephesians 6:10 "Finally, be strong in the Lord and in the strength of His might."
This strengthening of the Spirit comes to the degree we are filled with or influenced by the Holy Spirit (Ephesians 5:18). Moreover, the Spirit's strength is enjoyed and experienced as we position ourselves in a posture of prayer (Ephesians 6:18).
So how do we know that "the strength of his might" is most likely referencing the scriptures? First, the word of God itself is the offensive weapon of the otherwise defensive armaments in the spiritual armor of Ephesians 6:14-18. Second, Hebrews 4:12 ties together this concept of God's might and spiritual warfare - "For the word of God is living and active and sharper than any two-edged sword, and piercing as far as the division of soul and spirit, of both joints and marrow, and able to judge the thoughts and intentions of the heart." Then thirdly, 2 Corinthians 6:7 alludes to carrying forth spiritual weaponry in the right hand and the left, which in context includes the word of God.