For though I be absent in the flesh, yet am I with you in the spirit, joying and beholding your order, and the steadfastness of your faith in Christ.
Some of the adjectives used to describe steadfast is unwavering, resolute, firm, constant, dependable, and faithful. Paul was encouraging the Colossians believers to remain steadfast in their faith in Christ even though he wasn't present with them in the flesh, but was always with them in the spirit. This was because the Colossians believers as do all believers sometimes need encouraging from our mature Christian brothers and sisters.
Christians both then and now are engaged in a spiritual warfare designed by Satan and his army to impede kingdom building and the spread of the gospel of Christ. One of Satan's tactics is placing doubt in the minds of all who he can deceive with his lies. Therefore, Christians may become discouraged, but with encouragement from others and with the aid of the indwelling Holy Spirit believers can remain committed to Christ and His message. To remain steadfast in our faith all believers are to recognize Satan's tactics for what they are and stay focus on our mission and message, which is Christ Jesus.
Christ left His Spirit to aid believers in standing firm in faith and persevere until He return for His church. Therefore, all believers are outfitted with God's armour of protection so that we will remain steadfast in faith.
Steadfastness in Christ is the believer's unwavering commitment to Him.