Does God expect Christians to be perfect?
The short answer is yes and no.
The yes answer is based on Matthew 5:48 “Therefore you are to be perfect, as your heavenly Father is perfect” (NASB).
Jesus was telling us that God is the standard against which everything else is measured. Specifically, we are to love our enemies so "that you may be sons of your Father in heaven" (Matthew 5:45a HCSB).
The use of “perfect” here means complete. God loves all people, even evil people. This is how we can be as perfect as God. Our love for our fellow man needs to grow and mature to even include loving our enemies. If we do not love our enemies we are not behaving as sons of God should.
The answer is also no. We've all heard the sayings, “Nobody's perfect” and “Christians aren't perfect, just forgiven.”
God doesn't expect us to be perfect in the sense that we never sin. He knows we sin and has made provision for us for that through Jesus' high priestly work (1 John 2:1). Some Christians believe we can become perfect in the sense that we no longer sin. But the only way to believe that is to redefine sin as something less than it is, or reject the words in 1 John 1:8, “If we say that we have no sin, we are deceiving ourselves and the truth is not in us” (NASB).
No matter how hard we try we sin constantly and are therefore far from perfect. We commit sins of commission—doing that which we shouldn't, and sins of omission—not doing that which we should. I may sin by stealing or taking the Lord's name in vain. And I may sin by failing to rejoice, or to love God with all my heart, soul, mind, and strength.
God sees and knows our shortcomings. And that is why in daily life we need His undeserved favour—grace. In spite of us, His infinite love is unconditional. Our relationship to God is not based on our perfection, but on Christ's. His perfect obedience is credited to us so when God looks at us, He sees us as perfect. If we could be perfect on our own strength, Christ's death would have been unnecessary.
These two answers actually do fit together. The standard believers are to live by is our Heavenly Father's, who loves completely. Perfectly. Jesus taught that we must demonstrate love to all people, no matter what faith, nationality, or personality. If you love your enemies you then truly are perfect, complete, like your heavenly Father.
Will we ever achieve loving perfectly like our heavenly Father loves? Not in this life. But this is to be our goal and we are to pursue it wholeheartedly. Perfect love is a standard impossible for us to attain by our own efforts but what is impossible for man is possible with God. It's only through the power of God's Spirit His people can truly love and pray for those who intend to do them harm (Romans 12:14-21).
I will get nowhere if I trust in my own abilities. That which God demands, only He can accomplish, including the demand to love our enemies. What is impossible for man becomes possible for those who give their lives to Jesus Christ through the power of the Holy Spirit who lives in our hearts. For “I have been crucified with Christ and I no longer live, but Christ lives in me. The life I now live in the body, I live by faith in the Son of God…” (Galatians 2:20 NIV).
When I accept my imperfection, understand my inability, and receive God's grace I will be able to love all men in a way that is characteristic of our heavenly Father.
And that is what God expects.
I hope this helps.