Your spirit is described in the Word as the inner man, the hidden person of the heart, and the real you that became new when you accepted that Jesus Christ died for you and you received Him as Lord (comparable to Boss or ruler) of your life. Your spirit is much like the voice of God, which Elijah heard as a still small voice, but nevertheless, undeniable. It is that inner witness or peace, your "knower" that just has a surety of God's presence and His direction. The Holy Sprit reveals truth to your spirit, and communicates or bears witness (gives evidence) to your spirit in order to guide or lead you into God's will.
Jesus, in his discussion with Nicodemus in John 3, declares that what is born of the Spirit is spirit. In other words, building up your spirit is something only God does. The principle of "What you sow is what you shall reap" is demonstrated in the building up of our spirit. As we choose to obey His Word and the instructions given, the Holy Spirit, strengthens and edifies our spirit. A picture of God's kingdom in Hebrews 12 describes "the spirits of just men made perfect."
Therefore, it is important to note the specific Biblical steps or actions that God has promised to reward by strengthening our spirit. Let's consider four fruitful ways to cooperate with the Spirit of God that produce growth.
By far, the most direct way given in Scripture is found in 1 Corinthians 14:4, "he who speaks in a tongue edifies himself." Clearly praying in the spirit bypasses the mind, for the Word declares we are uttering mysteries in the spirit which the mind does not understand. Paul wished everyone prayed in tongues. Jude talks about the difficult times coming yet gives valuable instruction so we do not fall in the evil day, "But you, beloved, building yourselves up on your most holy faith, praying in the Holy Spirit, keep yourselves in the love of God..." Obviously tongues is not the final goal, rather an essential step to allow God to edify and build up our spirit so we can overcome the flesh and the world and rather be transformed into the likeness of and can have the ability to walk like Jesus.
Secondly, Jesus declares that the words He speaks are spirit and life (John 6:63). Paul commends the Ephesians (Acts 20:32) "to God and to the Word of His grace, which is able to build you up, and to give you an inheritance among all them which are sanctified." So when we take steps to let the Word dwell in us richly, the Holy Spirit who is the author of Scripture, can reveal Jesus, His nature and heart. God's Word is nourishment and life for the spirit, truth to renew the mind (Romans 12:2) and convert the soul (Psalm 19:7) and direction how to present our bodies as living sacrifices (Romans 12:1).
Third, God gives grace to the humble. When we pray, we humbly acknowledge our need for God and declare His promises trusting Him to do it. Taking time to seek God, to enter His presence with thanksgiving and praise, and to worship or surrender all that we are to Him, allows the Spirit of God to give grace which empowers us. Be still and know that I am God (Psalm 46:10)
Fourth, in Romans 8:13 where Paul describes the spiritual battle between spirit and flesh, we are instructed, "if by the Spirit you put to death the deeds of the body, you will live." Jesus describes fasting as a way to become a new wineskin that can hold the new wine. Fasting, when led by the Holy Spirit, along with focusing on God's Word, is a strong way of feeding the spirit man and starving or denying the flesh from dictating your actions. Choosing to obey the spirit rather than feed the flesh demonstrates who rules your life. Setting the mind on the flesh (just what it wants) is death, but setting the mind on the spirit is spirit and life. Parallel to obeying the Spirit in fasting, is obedience to Spirit-leading in any other matter, which exercises our "spirit" muscles from strength to strength, and gives newness of life.
Scripture is filled with examples of people who were mighty in spirit and able to accomplish great things in God. We too "can do all things through Christ who strengthens me." Paul prayed for us in Ephesians 3:16, "That He would grant you, according to the riches of His glory, to be strengthened with might through His Spirit in the inner man."
The day is coming, and now is, when the deceitful philosophy of the world, the pattern of living for our own fleshly desires, and the rejecting God's standards for holiness has released a flood of decadence in the earth. The morals of our society does affect us. Jesus painfully said, "many will fall away." What will keep us from succumbing to this increasing pressure? The key is to be strong in our spirit, our inner man, so we have the ability and strength to discern and reject the "lusts of the flesh, fulfilling the desires of the body and of the mind," (Ephesians 2:3). Unless God builds the house, unless we choose to let the Spirit build our spirit, our mind and flesh will dominate and we, like Solomon, will be drawn away from the Lord and His truth.
My heart cry (and the cry of the Spirit!) is for you is to build yourself up in the spirit, that "inner person of the heart" that is "very precious in the sight of God" 1 Peter 3:4