What this consisted in was greatly discussed in ancient philosophy. Varro enumerated 288 answers to the question. By Plato "the good" was identified with God.
In the New Testament the true "good" is placed by Jesus in "the kingdom of God" (Mt 6:33; 13:44 f, etc.). This means nothing earthly merely (Mt 6:19), but heavenly and eternal. It implies the Old Testament conception that God is the true "good"; for to seek the Kingdom supremely means whole-hearted devotion to God as our heavenly Father and to His righteousness. It was also spoken of by Jesus, as sonship to the heavenly Father (Mt 5:45, etc.). This "good" is not something merely to be given to men, but must be sought after and won through taking up a right attitude toward God and our fellows, cherishing the Love that God is, and acting it out in kindness and righteousness, in resemblance to our God and Father (Mt 5:43-48; here Ge 1:27 is implied).
In some of the epistles Christ is represented as the true "good" (Php 3:8 f; Col 3:1-4,11). This is because in Him God was manifested in His Truth and Grace; in Him "the Kingdom" was present; through His cross the world is so reconciled to God that men can find acceptance and rest in Him as their "good"; Christ Himself in the Spirit is our Life; in Him we have "God with us." Having God as our "good," nothing but good, in the truest and highest sense, can come to us. Even the most seemingly adverse things are turned into good "to them that love God" (Ro 8:28).
Our true "good" is found thus in God even in this present life; but its fullness can be realized only in the eternal life beyond. Placing our "good" in God leads to such life in devotion to the "good" that God is, as tends to bring all that is best to this present world. It is men’s failure to do this that is the source of our misery (Jer 2:13, etc.). The ultimate ideal is that God shall be "all in all" (1Co 15:28).