Our Scripture reading today is Ephesians 3:16-17.
Verse 16, "That he would grant you, according to the riches of his glory, to be strengthened with might by his Spirit in the inner man;"
At the moment we believe in the Gospel (death, burial, and resurrection of Jesus Christ) for our eternal salvation, we are in dwelt by the Spirit of God. The Holy Spirit will be in us until the moment we enter the presence of God in Heaven. When it comes to our salvation, we have eternal security.  
The more that we yield to and walk in the Spirit, the stronger our faith will become.  He is strengthening our inner man.  Strong faith does not come to us because we are strong men and women.  2 Corinthians 12:9, "And he said unto me, My grace is sufficient for thee: for my strength is made perfect in weakness. Most gladly therefore will I rather glory in my infirmities, that the power of Christ may rest upon me."  The sooner we realize that we are weak and in need of Spirit's power, the quicker our faith will be strengthened.  Zechariah 4:6, "Then he answered and spake unto me, saying, This is the word of the LORD unto Zerubbabel, saying, Not by might, nor by power, but by my spirit, saith the LORD of hosts."
Strong faith cannot be worked up in the power of the flesh.  Strong faith will be developed as we yield to the working of the Holy Spirit in our lives.
Your Friend,
Pastor