What does it mean to be "in Christ"?

For 2017, the phrase I am focusing on is "in Christ."  Each week, I will post verse(s) that includes the phrase "in Christ". I look forward to growing in understanding of what it means to be "in Christ."

1 Paul, an apostle of Christ Jesus by the will of God according to the promise of the life that is in Christ Jesus,

² To Timothy, my beloved child:
Grace, mercy, and peace from God the Father and Christ Jesus our Lord.
³ I thank God whom I serve, as did my ancestors, with a clear conscience, as I remember you constantly in my prayers night and day. ⁴ As I remember your tears, I long to see you, that I may be filled with joy. ⁵ I am reminded of your sincere faith, a faith that dwelt first in your grandmother Lois and your mother Eunice and now, I am sure, dwells in you as well. ⁶ For this reason I remind you to fan into flame the gift of God, which is in you through the laying on of my hands, ⁷ for God gave us a spirit not of fear but of power and love and self-control.
⁸ Therefore do not be ashamed of the testimony about our Lord, nor of me his prisoner, but share in suffering for the gospel by the power of God, ⁹ who saved us and called us to a holy calling, not because of our works but because of his own purpose and grace, which he gave us in Christ Jesus before the ages began, ¹⁰ and which now has been manifested through the appearing of our Savior Christ Jesus, who abolished death and brought life and immortality to light through the gospel, ¹¹ for which I was appointed a preacher and apostle and teacher, ¹² which is why I suffer as I do. But I am not ashamed, for I know whom I have believed, and I am convinced that he is able to guard until that day what has been entrusted to me. ¹³ Follow the pattern of the sound words that you have heard from me, in the faith and love that are in Christ Jesus. ¹⁴ By the Holy Spirit who dwells within us, guard the good deposit entrusted to you. (2 Timothy 1:1-14)