Philippians 2:13 is written to believers after the day of Pentecost.  It is written to those who have, according to Romans 10:9-10, confessed with their mouth the Lord Jesus and believed in their heart that God raised him from the dead.  It is written to the church of our day and time.  It is written to you and me.
    Once a believer gets born again, it is God that is at work within both to will and to do His Word.  Only God can really will.  Only God can really do.  It is His strength energized in us that makes us more than conquerors in every situation.  It is God's ability to do in us that gives us the victory.  The word "worketh" is the Greek word "energeo".  It means to energize.  It is the power of God in us that is energized as we believe His Word.
    Now, we know from the Word of God that our God never MAKES us do anything.  God gives us the ability.  God gives us the strength to do His Word.  But God also has limited himself to our believing and freedom of will.  If we are going to do His will, we must get to the point that we know and believe that God is in Christ in us to will and to do.

Ephesians 3:20
   Now unto him that is able to do exceeding abundantly above all that we ask or think according to the power that worketh in us,

   Only God can really DO.  God is ABLE TO DO all that we ask or think according to the power [dunamis] that worketh [energeo] in us.  Dunamis is God's inherent power in us.  It is God's ability to do waiting to be energized in us as we believe His Word.
    When we think according to His Word, and we ask according to His Word, God's power is energized in us and we are able to do ALL because of His ability to do in us.
    Ephesians 3:20 living is even greater than God doing all we ask or think according to His Word.  It is God's ability to do in us ABOVE ALL.  It is God's ability to do in us SUPERABUNDANTLY ABOVE ALL.  It is God's ability to do EXCEEDING SUPERABUNDANTLY ABOVE ALL.  We do according to God's ability to do in us just as Jesus Christ did according to God's ability to do in him.

John 5:19,30
   Then answered Jesus and said unto them, Verily, verily I say unto you, The Son can do nothing of himself, but what he seeth the Father do: for what things soever he doeth, these also doeth the Son likewise.
   I can of mine own self do nothing: as I hear, I judge: and my judgment is just; because I seek not mine own will, but the will of the Father which hath sent me.

    It is God that has the ability to do.  When we line up our thinking and action with God's Word, we also CAN DO.  Many times we look at our own inability to do in a situation and condemn ourselves for our lack of strength.  Believing is having knowledge from God and acting on that knowledge.  When you believe the stock broker who tells you that a certain stock is a good buy - you buy the stock.  If you do not believe him, you do not buy the stock.  Believing is acting on knowledge.  It is not in man to save himself.  It is not in man to do the works of God's Word without God.  When we have a need (physical, mental, or spiritual) we must go to God's Word to know what God would have us to do.  We ask and think according to the knowledge of God and then it is God that energizes His ability to do in us.
 
Colossians 1:27
   To whom [us] God would make known what is the riches of the glory of this mystery among the Gentiles; which is Christ in you, the hope of glory:

   It is the same Christ that acted so boldly upon the knowledge of God in him that is IN US by way of the holy spirit.  We have God in Christ in us.  The greatness of this truth is that God is at work in us to do.  With God in Christ in us we are more than sufficient for any of life's situations.   With Christ in us we have the ability to do as he did.

Philippians 4:13
   I can do all things through Christ which strengtheneth me.

   A literal translation of this verse according to Biblical usage is that I am strong for all things and equal to all things through Christ who infuses inner strength in me.  Paul was self adequate in every situation because it was God's ability to do in Christ that was energized in him as Paul did God's Word.  We can do because God can do.