The works that the legalists would require are a gift from God given to the believer.
Obedience is a gift.
Repentance is a gift.
Grace is a gift.
Salvation is a gift.
The Holy Spirit is a gift.
They are all the work of God in the believers life.
The Lord Jesus is the Author and Finisher of our faith. He starts our faith, He works all the middle parts, and He finishes our faith.
And That is a Gift.
That is right, ALL are a gift .
Justification comes from understanding of much more than just The Cross. There's more, for starters, the Holy Spirit 'reception' at His appointed time, NOT yours. And, no one, no, not even one of us, knows when that time He entereth in to our body, but Him that knoweth ALL things, created ALL things, knows, and, fear of the Lord is the beginning of knowledge and with it comes understanding of the Holy One.
Use His gifts given right. The Lord leads. Follow. He will show you great and unspeakable things, even the deeper things of God. Let the Spirit lead, He knows how to help you best bring glory to God and He will never leave you nor forsake you IF YOU ARE FAITHFUL and are doing His will , which means never leaving nor forsaking Him