Reason Not To Sin - 1 Peter 1:15 - Called by God

but as he who called you is holy, you also be holy in all your conduct
1 Peter 1:15, ESV
 

Why not sin?

We were called by God. He has a purpose for us, not to subject us to slavery and things we don't want to do (Rom 8:15). Rather, He has a purpose that makes us free and joyful. When sin entered the world, man and nature were subjected to vanity (Rom 8:20), but God's goal for you now is not vanity but fulness in Christ (Col 2:10). "He who calls you is faithful; he will surely do it." (1 Thess 5:23-24, Phil 1:6).

What a hope we have! What grace to be brought to us at the revelation of Jesus Christ (1 Pet 1:13)!

God will surely do this independent of you, but you won't find joy in God's commands of holiness unless you consider Him faithful who promised, as Sarah did (Heb 11:11)—you won't find power to sanctify yourself or stay away from sin unless you trust in God's power and purpose of holiness during each temptation.