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."

2 You then, my child, be strengthened by the grace that is in Christ Jesus, ² and what you have heard from me in the presence of many witnesses entrust to faithful men, who will be able to teach others also. ³ Share in suffering as a good soldier of Christ Jesus. ⁴ No soldier gets entangled in civilian pursuits, since his aim is to please the one who enlisted him. ⁵ An athlete is not crowned unless he competes according to the rules. ⁶ It is the hard-working farmer who ought to have the first share of the crops. ⁷ Think over what I say, for the Lord will give you understanding in everything.

⁸ Remember Jesus Christ, risen from the dead, the offspring of David, as preached in my gospel, ⁹ for which I am suffering, bound with chains as a criminal. But the word of God is not bound! ¹⁰ Therefore I endure everything for the sake of the elect, that they also may obtain the salvation that is in Christ Jesus with eternal glory. ¹¹ The saying is trustworthy, for:

If we have died with him, we will also live with him;
¹² if we endure, we will also reign with him;
if we deny him, he also will deny us;
¹³ if we are faithless, he remains faithful—

for he cannot deny himself. (2 Timothy 2:1-13)