The ultimate purpose of man must not, it seems, be tied to that which is not ultimate. It is true that God does give mankind commands such as "Be fruitful and increase in number".
However, it is important to note that mankind's fulfillment of this command did not prompt God's greatest act. It was rather the separation of mankind from God through sin that prompted God to become incarnate, die and rise again. The entire Bible focuses on the redemption of mankind through the death, burial, and resurrection of Jesus Christ. So, it is instructive to note what this accomplished. The key thing, it seems, is the restored relationship. God wanted mankind to be in fellowship/union/relationship with Him.
And this is eternal life, that they know you the only true God, and
Jesus Christ whom you have sent. John 17:3 ESV
Father, I desire that they also, whom you have given me, may be with
me where I am, to see my glory that you have given me because you
loved me before the foundation of the world. John 17:24 ESV
But to all who did receive him, who believed in his name, he gave the
right to become children of God... John 1:12 ESV
Then we who are alive, who are left, will be caught up together with
them in the clouds to meet the Lord in the air, and so we will always
be with the Lord. 1 Thessalonians 4:17 ESV
In my Father’s house are many rooms. If it were not so, would I have
told you that I go to prepare a place for you? And if I go and
prepare a place for you, I will come again and will take you to
myself, that where I am you may be also. John 14:2-3 ESV
So, if we look at the greatest act of God in all time--the atonement through the death, burial and resurrection of Jesus Christ--it becomes apparent that all of this was done to restore a relationship between God and mankind. So, we were created to know Him, to abide in Him, and to be with Him forever.