Amen. Your brother in Christ.
The doctrine "Union With Christ" underlines every aspect of the whole salvation (according to 2 Timothy 2:10 “…obtain the salvation that is in Christ Jesus”) which reveals a detail Scriptural pattern of salvation (and according to 2 Timothy 3:15 “…make you wise for salvation through faith in Christ Jesus”). The doctrine itself carries the whole salvation package from "Election” (Ephesians 1:4) all the way up to “Glorification" (Colossians 1:27). This "union" is between Christ and his elect, which was planned in eternity by the divine counsel and foreknowledge through his sovereignty. In which, Christ was chosen to be our Savior before the creation of the world (1 Peter 1:20, Ephesians 3:11, 1:4, 11) by the provision of Christ through the application of the Holy Spirit.
Philippians 2:1 Therefore if you have any encouragement from being UNITED WITH CHRIST, if any comfort from his love, if any common sharing in the Spirit, if any tenderness and compassion,
1 Corinthians 6:17 But whoever is UNITED WITH THE LORD is one with him in spirit.
The “union” is indicated by the preposition “in” (Paul’s language usage, like: “in Christ,” “in Him,” “with Christ,” and “through Christ” etc.) which carries a wide range of implications in a Soteriological sense. The phrase "in Christ" is also used in the sense that you are a CHRISTIAN (Romans 16:7, Ephesians 1:13). Paul also uses another type of language like "created in Christ" (2 Corinthians 5:17, Galatians 6:15, Ephesians 2:10), even our identification is symbolically represented in water baptism, and uses a certain phrase "baptized into Christ" (Galatians 3:27) in reference to our Union With Christ, like "Crucified With Christ," "Buried With Christ," "Raised With Christ," and "Alive With Christ" (Galatians 2:20, Romans 6:3-5, Colossians 2:11-13). And we are encouraged to "set your hearts on things above" (Colossians 3:1-3) and "Seated With Him" (Ephesians 2:6).
The "Union With Christ" in the Soteriological pattern would go something like this:
⦁ Election (Ephesians 1:3-4)
⦁ Regeneration (Ephesians 2:5, Colossians 2:13)
⦁ Faith (Galatians 2:20, Ephesians 3:16-17)
⦁ Justification (2 Corinthians 5:21, Philippians 3:8-9)
⦁ Sanctification (1 Corinthians 1:30)
⦁ Adoption (Galatians 3:26)
⦁ Eternal Security (Romans 8:38-39)
⦁ Glorification (Colossians 3:4, 1 Thessalonians 4:16-17)