'If God were your Father, you would love me.' John 8:42
Some of the verses in John are indescribably beautiful and easy to understand - this is one of them!
You can start by asking yourself the question, 'Do I love Christ?'
If the answer is yes, then you have the reassurance that God is your Father, and that you are a child of God. What blessing and security is in this thought!
If your answer is 'No' then you need to accept the truth as it is written in the Bible that you are not a child of God. Your argument doesn't lie with me but with the Son of God. Face the truth and there is time to change.
If your answer is 'I don't know' take time to find out. We cannot love Christ the way we love another human being but, there are certain principles that will help you to know. First of all, would you exchange Christ for a million pounds? If someone were to offer you the holiday of a lifetime but you could only receive it if you decided not to be a Christian anymore - would you take the holiday or Christ? You will never truly love Christ with a soppy, sentimental love but if you can answer these questions positively in favour of your faith then you have the reassurance that you too are a child of God. God is your Father and Christ your Lord and Saviour.
Learn to love Him. Satan hates when people love Christ with a loyalty and consistency that reflect in their lifestyle because this is what makes the true church of Christ.