Oneness does NOT mean you do not have a self or free will.
God, Who encompasses all being, created beings who have everything individually, but who want to share it to increase their joy. (T-4.VII.5:1)
God created His Sons by extending His Thought, and retaining the extensions of His Thought in His Mind. All His Thoughts are thus perfectly united within themselves and with each other. (T-6.II.8:1-2)
Creation is the sum of all God's Thoughts, in number infinite. (W-pII.11.1:1)
God knows His children with perfect certainty. He created them by knowing them. (T-3.III.7:9-10)
In the creation, God extended Himself to His creations and imbued them with the same loving Will to create. (T-2.I.1:2)
The constant going out of His Love is blocked when His channels are closed, and He is lonely when the minds He created do not communicate fully with Him. (T-4.VII.6:7)
What God does know is that His communication channels are not open to Him, so that He cannot impart His joy and know that His children are wholly joyous….God's extending outward, though not His completeness, is blocked when the Sonship does not communicate with Him as one. So He thought, "My children sleep and must be awakened." (T-6.V.1:5,7,8)
When the Atonement has been completed [and we are back in Heaven], all talents will be shared by all the Sons of God. (T-1.V.3:1)
When the Atonement is complete and the whole Sonship is healed…the Holy Spirit will remain with the Sons of God, to bless their creations and keep them in the light of joy. (T-5.I.5:5,7)
The Holy Spirit promotes healing by looking beyond it to what the children of God were before healing was needed, and will be when they have been healed. (T-5.II.1:2)
God has but one Son, knowing them all as one. (T-9.VI.3:5)
It should especially be noted that God has only one Son. If all His creations are His Sons, every one must be an integral part of the whole Sonship. The Sonship in its oneness transcends the sum of its parts. However, this is obscured as long as any of its parts is missing. That is why the conflict cannot ultimately be resolved until all the parts of the Sonship have returned. (T-2.VII.6:1-5)
It should be noted that God has begotten only one Son. If you believe that all of the Souls that God created are His Sons, and if you also believe that the Sonship is One, then every Soul must be a Son of God, or an integral part of the Sonship. You do not find the concept that the whole is greater than its parts difficult to understand. You should therefore not have too great difficulty with this. The Sonship in its Oneness does transcend the sum of its parts. However, it loses this special state as long as any of its parts are missing. This is why the conflict cannot ultimately be resolved until all of the individual parts of the Sonship have returned. Only then, in the true sense, can the meaning of wholeness be understood.
One brother is all brothers. Every mind contains all minds, for every mind is one. Such is the truth. Yet do these thoughts make clear the meaning of creation? Do these words bring perfect clarity with them to you? What can they seem to be but empty sounds; pretty, perhaps, correct in sentiment, yet fundamentally not understood nor understandable. The mind that taught itself to think specifically can no longer grasp abstraction in the sense that it is all encompassing. We need to see a little, that we learn a lot. (W-pI.161.4:1 8)
When you are told what is natural, you cannot understand it. The recognition of the part as whole, and of the whole in every part is perfectly natural, for it is the way God thinks, and what is natural to Him is natural to you. (T-16.II.3:2-3)