Mathematics has several named properties. The commutative property, for instance says that “changing the order of the operands” does not change the result. Thus, a+b=b+a (and the same holds true for multiplication). The distributive property says if you multiply a+b+c by a number, you get the same result if you multiply each of those by that number and then add them together. The associative property says that if you add three or more numbers, the result is the same regardless of the order you add them. Then there is the transitive property. It says that if a=b and b=c then a=c. Of all the properties, this is the one that Jesus uses in his prayer in John 17.
That they all may be one; as thou, Father, art in me, and I in thee, that they also may be one in us: that the world may believe that thou hast sent me. And the glory which thou gavest me I have given them; that they may be one, even as we are one: I in them, and thou in me, that they may be made perfect in one; and that the world may know that thou hast sent me, and hast loved them, as thou hast loved me. (Jn 17:21-23)
Jesus starts out using the commutative property. “Thou, Father, art in me, and I in thee.” He says A=B, where A is God and B is Jesus (thou art in me) and then commutes it, B=A (I in thee). Some people have alleged that Jesus never claimed to be God or the Son of God. Those people have obviously never read the gospels. “I and the Father are one.” (Jn 10:30) Lest some argue that he simply means they are one in purpose, the witnesses at Jesus’ trial testified, “He said, I am the Son of God.” (Matt 27:43) Even if he had not said it, the unclean spirits he cast out of people consistently testified, “Thou art the Son of God.” (Matt 8:29; Mk 3:11; Lk 4:41; 8:28) A=B and B=A.
The second part of the Transitive Property then requires that Jesus (b) and his followers (c) are equal. In the passage quoted above, Jesus states this as a given, requiring no proof. “I in them.” Some people point out that Jesus is the “only begotten of the Father.” (Jn 1:14) They then refer to the believers as having been adopted (Rom 8:15; Gal 4:5; Eph 1:5), as if that makes everyone of less value than Jesus. The fairy tales often show stepchildren as being looked down upon, but we are not stepchildren. We have received adoption. Many videos are available online, showing the joy of a child who has been a stepchild for a while being given the gift of adoption. Legally, adoption places a person on equal footing with the birth-children in a family. We are not less than Jesus; we are equal as brothers and sisters in the family. B=C, not B is greater than C.
Having established that A=B and B=C, we must necessarily reach the conclusion Jesus reached, that A=C. “That they also may be one in us.” God, Christ, and Christians are then a unity. I am in God. Not through any righteousness of my own, but through that given by Jesus. “But to him that worketh not, but believeth on him that justifieth the ungodly, his faith is counted for righteousness.” (Rom 4:5)
Is being in God something about which we should boast? Yes, and no. We boast of our righteousness through the blood of Jesus. We rejoice that we are no longer slaves to sin. Even though we are one with God and Jesus, though, we should be humbled. We did not earn unity with God and Christ. It was granted to us through faith. We can rejoice that we are in the family of God, but we should also be humbled that God counts us worthy to be accepted into that family.