My friend says that we're either doing God's will or we aren't doing God's will, and there isn't anything in between. But we're never perfect, are we? So how can we ever say we're doing God's will completely, when we're probably only doing it halfway?
You are right up to a point; even our most sincere attempts to do God’s will are imperfect and inadequate, and tainted by our sinful nature. Jesus warned His disciples, “So you also, when you have done everything you were told to do, should say, ‘We are unworthy servants; we have only done our duty'” (Luke 17:10).
But don’t forget two important truths. First, God is able to take even our feeble efforts and use them for His glory. We don’t have to be perfect before God can use us! Do you remember the little boy who gave his lunch to Jesus? (You can read about him in John 6:5-13.) His lunch consisted of only five small loaves of bread and two fish – but Jesus miraculously multiplied it and fed an entire crowd of 5,000. In the same way, God can take even our smallest efforts and use them to bless others.
The second truth is that by His Spirit God can give us the strength we need to do His will. As the Bible says, He “is able to do immeasurably more than all we ask or imagine, according to his power that is at work within us” (Ephesians 3:20).
Seek God’s will… ask God for the strength to do His will… and then diligently do it to the best of your ability. Then thank Him for using you in spite of your sins and shortcomings – and leave the results in His hands.