What is the faithfulness of God, and to whom is He faithful? Faithfulness is part of His character; He never deviates from who He is and He always fulfils what He has promised. He is true to His Word. Because of God's unchanging nature Father, Son and Spirit implicitly trust one another other (Hebrews 3:2). Because of God's faithfulness to Himself, we can trust His every Word and be totally certain that His promises will be fulfilled.
 
The God of peace will bring peace to all who submit to Him; the absence of hostility between us and Him is because our sins are paid for and forgiven, so that we can be made holy (special for Him) in every part of our lives. God never demands more payment than Jesus has already paid on our behalf; that would be unjust (1 John 1:9). God's grace turns sinners into saints, because that is God's purpose for His people (Romans 1:7).
 
We are not just animals. We have bodies as they do, but different. We have a very different mind with deep desires and ability to choose (which is reflected here by the word 'soul'), and we also have a God-consciousness which is unique to human beings (spirit). In the believer, all three elements of humanity are being transformed (2 Corinthians 3:18) by God's Spirit who is at work within us (Ephesians 3:20). God has determined to make us ready to meet Him, and He has the power to do it (Philippians 1:6).
 
God, who has called us to belong to Him, knows that we cannot ever make ourselves clean or holy. That is why Jesus came to die for us and the Holy Spirit has been given to sanctify us. When we despair of ourselves, we should realise that God never despairs of His ability to make us like Jesus. Yes, He wants us to cooperate with Him, but the transforming power is His. And even when we are unfaithful to Him, He remains faithful to His purpose of making us holy because He cannot deny His own character (2 Timothy 2:13). What amazing grace! We do not deserve it and sometimes we do not really want it, but God is at work in us to change us from the inside (Philippians 2:13). Thank Him and stop fighting against what He is doing in you: start cooperating for your blessing and His glory.