"The knowledge that we are in Christ and that the Father accepts us as in Him is a sure foundation for effective prayer." (Wentworth Pike in Principles of Effective Prayer)
Unfortunately, many believers do not fully grasp this truth. So they have times when they feel their prayers are not effective, and they become discouraged. Sometimes to the point where they give up and walk away from their faith in Christ to their old sinful ways. What a shame!
If we accept and humbly live by this one principle that we have a position of authority in Christ Jesus, it will revolutionize our praying and many other aspects of our Christian life. Do take time to study this - especially in the book of Ephesians - until you see the wonder of it, and by faith make it yours.
Paul uses this phrase, "in Christ" many times in the book of Ephesians so that is a great place to start your study. Further, I Corinthians 1:30 explains, "It is because of Him that you are in Christ Jesus, who has become for us wisdom from God - that is, our righteousness, holiness and redemption." Christ Himself is the HEAD of His Body, the Church. Therefore, all who believe and receive Him as their personal Saviour, are made a part of His Body, the Church universal. That is the One True Church across denominational lines, and if your local church is Biblical it is part of it too, for it is comprised of all true believers in Christ Jesus.
When you trust Jesus Christ to be your personal Saviour, you are baptized, or spiritually put in Christ. This is not a matter of location, like when you say, "I am in my home village," or "I am in Kibaha, Tanzania." Being "in Christ" means we are under His headship over his Body. It means we live as Christ, the Head, tells His Body to live. So if Christ, the Head, tells us to forgive our brother, or to confess some sin, or to go preach there, or to keep quiet when falsely accused, then we simply obey the way an arm or a leg would obey the head of its body.
Being part of a body means that all the parts are connected to the same blood vessels and nerves. They are fed and kept alive from the same source. If you cut off a foot, it is no longer connected to the body, so it dies.
However, since we believe in Christ for salvation, God makes us part of Jesus' Body, (also known as the Church), and as long as we stay in fellowship with His Body, we can draw spiritual strength and health and wisdom from the Head. - Oh, let us willingly desire to be "in Christ" and to be in harmony with the other parts of His Body. Let us listen for directions from our Head, in Christ, and obey as soon as we understand what He wants us to do.
There is more to being "in Christ Jesus" - it becomes especially glorious and wonderful in prayers of intercession! Romans 8:34 says, "...Christ Jesus, who died - more than that, who was raised to life - is at the right hand of God and is also interceding for us." So not only did we die in Christ, but we also rose and ascended and are seated at the right hand of God - all in Christ.. (See Ephesians 1:20-23 for more).
"Our identification with Christ was not confined to His death but includes His resurrection (Eph. 2:5) and ascension also... (v.6) He sits in the place of authority at the right hand of the Father (Rom.8:34) and we with Him. From this stem our present throne rights. These carry with them potential powers and privileges altogether too few of us have entered into." So wrote Theodore H. Epp in Praying with Authority
If we are truly abiding in Christ we are seated with Him at the right hand of the Father-God, and "in Christ" can intercede for the people here who burden our hearts. In Christ Jesus we have that power and authority. If we have truly died to our sins in Christ, we are also alive in Him by His ressurrection power, and also with Christ in Heavenly places. This great truth is hidden from the unworthy and the sinful, and revealed only to those who earnestly, humbly, seek to know and experience it.
Now you may be asking, "Tell me again, how can I be sure I am in Christ?"
Abide in Christ by hungrily studying His Word with the goal of obeying it. But don't let it become 600 laws to you that you must somehow keep. The essence or sum of all the laws, as Jesus told His disciples, is that we always think, say and do the most loving thing, the most loving way.
The whole purpose of this great truth, as we read in John 15, is that we bear spiritual fruit - fruit that will remain for time and eternity. Before anything else, it will show up in our effective prayers. All because we are "in Christ."