Something in our self-righteous flesh convinces us that salvation is earned by good conduct, or by observing religious practices like keeping ‘holy days’ or other rituals. Grace and human effort do not provide forgiveness of sin. Salvation is not the result of the law plus grace, or legalism plus grace.
Salvation, from start to finish, is the work of Christ on behalf of fallen man. The Galatians began in the Spirit, but slipped into trying to develop their faith by following the law. (Gal 3:3) Likewise, the Corinthian church began in the Spirit, but abused the grace of God with unholy, unruly behavior. (1 Cor 1:2; 5:1; 11:17-22)
The grace of our Lord Jesus eliminates the need to perform fleshly, legalistic deeds to earn or keep our salvation. Also, the Spirit of God convicts us of sin and enables us to walk in holiness.
It is truly all about trusting in Jesus and walking with Jesus. The new covenant isn’t about outward rituals, but about a new heart. The law does indeed point us to our need for Christ, but don’t turn back to follow it.