In order for him to execute His covenant engagement it was necessary for Christ to assume human nature and be made in all things like unto His brethren

Most blessedly were several features of the everlasting covenant typed out in Eden. Let us consider these features:

2. In order for him to execute His covenant engagement it was necessary for Christ to assume human nature and be made in all things like unto His brethren, so that He might enter their place, be made under the law, and serve in their stead. He must have a soul and body in which He was capable of suffering and being paid the just wages of His people’s sins. This explains to us that marvelous passage in Hebrews 10:5-9, the language of which is most obviously couched in covenant terms: the whole displaying so blessedly the voluntary engagement of the Son, His perfect readiness and willingness in acquiescing to the Father’s pleasure. It was at the incarnation Christ fulfilled that precious type of Himself found in Exodus 21:5. Out of love to His Lord, the Father, and to His spouse the church, and His spiritual children, He subjected Himself to a place of perpetual servitude.

Arthur W. Pink- The Divine Covenants-Part One-The Everlasting Covenant