A key to reigning in life is to stand on the truth that Christ lives in a believer. If you believe Jesus, you are united with Christ, and you can reign in life through him, who is the head over every power and authority. Do not think that Christ will reign for you. No, it is you who must reign though him who lives in you.
For if, by the trespass of the one man, death reigned through that one man, how much more will those who receive God's abundant provision of grace and of the gift of righteousness reign in life through the one man, Jesus Christ (Rom 5:17).
Note that the subject for the verb “to reign” is “those who receive God’s abundant provision of grace and of the gift of righteousness,” not God, or Christ, or even life. You reign because the one who lives in you has already defeated “death” and is now seated at the right hand of the Father with all authority and power given to him in heaven and on earth. So, now, together with Jesus, you are also seated at the right hand of the Father.
Do not think that it is difficult to be one with Christ or with God. The Bible says:
Do you not know that he who unites himself with a prostitute is one with her in body? For it is said, “The two will become one flesh.” But he who unites himself with the Lord is one with him in spirit (1 Cor 6:16-17).
You might think that it is a mark of elegance to say that you are one with God. No, it is not. Jesus said, “I and the Father are one (John 10:30),” yet, he is the humblest person of all. No truth per se makes you prideful. You become prideful by standing on your own ideas about yourself. Hearing Jesus say that, the Jews got mad, and tried to kill him.
When Philip asked Jesus to show them the Father, he answered:
Anyone who has seen me has seen the Father. How can you say, “Show us the Father”? Don't you believe that I am in the Father, and that the Father is in me? The words I say to you are not just my own. Rather, it is the Father, living in me, who is doing his work (John 14:9-10).
The expression, “I am in the Father, and… the Father is in me,” was his way of saying that he was one with the Father. He went on to say:
On that day you will realize that I am in my Father, and you are in me, and I am in you (v. 20).
Think what Jesus meant by “you are in me, and I am in you”? It surely is an amazing statement. It was not, however, the first time that he identified himself with somebody else in this way. Look at the following words, for instance:
And whoever welcomes a little child like this in my name welcomes me. But if anyone causes one of these little ones who believe in me to sin, it would be better for him to have a large millstone hung around his neck and to be drowned in the depths of the sea (Mat 18:5-6).