St Irenareus says:
>In the beginning, therefore, did God form Adam, not as if He stood in need of man, but that He might have [some one] upon whom to confer His benefits. For not alone antecedently to Adam, but also before all creation, the Word glorified His Father, remaining in Him; and was Himself glorified by the Father, as He did Himself declare, “Father, glorify Thou Me with the glory which I had with Thee before the world was.” Nor did He stand in need of our service when He ordered us to follow Him; but He thus bestowed salvation upon ourselves. For to follow the Saviour is to be a partaker of salvation, and to follow light is to receive light. But those who are in light do not themselves illumine the light, but are illumined and revealed by it: they do certainly contribute nothing to it, but, receiving the benefit, they are illumined by the light. Thus, also, service [rendered] to God does indeed profit God nothing, nor has God need of human obedience; but He grants to those who follow and serve Him life and incorruption and eternal glory, bestowing benefit upon those who serve [Him], because they do serve Him, and on His followers, because they do follow Him; but does not receive any benefit from them: for He is rich, perfect, and in need of nothing. But for this reason does God demand service from men, in order that, since He is good and merciful, He may benefit those who continue in His service. For, as much as God is in want of nothing, so much does man stand in need of fellowship with God. For this is the glory of man, to continue and remain permanently in God’s service. Wherefore also did the Lord say to His disciples, “Ye have not chosen Me, but I have chosen you;” indicating that they did not glorify Him when they followed Him; but that, in following the Son of God, they were glorified by Him. And again, “I will, that where I am, there they also may be, that they may behold My glory;” not vainly boasting because of this, but desiring that His disciples should share in His glory: of whom Esaias also says, “I will bring thy seed from the east, and will gather thee from the west; and I will say to the north, Give up; and to the south, Keep not back: bring My sons from far, and My daughters from the ends of the earth; all, as many as have been called in My name: for in My glory I have prepared, and formed, and made him.” Inasmuch as then, “wheresoever the carcase is, there shall also the eagles be gathered together,” we do participate in the glory of the Lord, who has both formed us, and prepared us for this, that, when we are with Him, we may partake of His glory.
God created us because He loves us and wants us to be deified, basked in His love and glorifying Him thus.
If Adam and Eve didn't screw up, the Son would have become incarnate (possibly from Eve) and, by taking onto our human nature, would have opened the way to deification for Adam and Eve, and the whole of humanity. Unfortunately, Adam and Eve mis-used their free will, and so God delayed His plan of sanctification, until a time He saw fit.