There is nothing missing or lacking in your relationship with God once you are in Christ.
As you have faith in what Christ has done for you, you will learn to manifest the truth of your identity and inheritance as a child of God. If you say, "I'm trying so hard to be a Christian," you're relying on your own self-efforts to measure your faith and spiritual growth. This will lead to burnout and spiritual exhaustion. This is due to trusting in your own confidence in building your Christian life.
Grace empowers you to live in humility. This is what Jesus taught us. Throughout His earthly ministry, our Lord illustrated the importance of remaining connected to and dependent on the Father:
I do nothing on my own but speak what the Father has taught me. The one who sent me is with me; He has not left me alone, for I always do what pleases Him.
John 8:28 (NIV)
Intimacy and dependency enable us to be teachable, to receive and apply God's truth in our daily life. Understanding that God is pleased with us because of Jesus' perfect sacrifice allows us to always do what pleases Him—for our Father has graciously bestowed upon us His Spirit in order for us to live a life pleasing to Him. Therefore, obedience is an act of love, not something legalistic.
The more we understand that we are loved by God, the more we will love God and be willing to surrender all to God. Holding back indicates the fear of losing out. The one who fears has not yet been made perfect in God's love. This makes us think of what we are giving up as a "sacrifice," not an honour, because we know that we already have all things in Christ.
When we give or serve—we are returning to God what He has first given us. It is His love working in and through us. It is extremely difficult, if not impossible, for us to live with any sense of boldness and authority unless we dwell in the gospel truth. Learn to walk in the light of the gospel and you will experience the joyful reality of who you are and what you have in Christ.