This verse indicates that there must be surrender in order to gain oneness.
The "if" there implies that our oneness in Christ is tentative and a choice.
It also says, "yourself", not your heart which we must give also.
Give up your will, goals, all the things of this life. Surrender to God.
If I say a little prayer and go on my merry little way in life just doing what
is right in my own eyes then I didn't surrender.
If I have been a Christian for years but God doesn't move much in my life I
may have not completely surrendered myself to Him.