Philippians 2:12,13 - Work Out Your Salvation with Fear and Trembling.

Phil 2:12 (KJV)  Wherefore, my beloved, as ye have always
obeyed, not as in my presence only, but now much more in my absence,
work out your own salvation with fear and trembling.
Phil 2:13 (KJV)  For it is God which worketh in you both to will
and to do of his good pleasure.

There are three aspects of the believer's salvation: (1) past
(justification), (2) present (sanctification), and (3) future (glorification).
[New Bible Companion]

Work out. used here in the sense of "to carry out to
completion." This does not endorse the idea of salvation by works. We are
saved by grace, through faith. But this grace leads us to good works.
Thus, such works are the outworking of the grace that has effected our
salvation. Many are attracted to the Christian way, but are unwilling to
meet the conditions by which the reward of the Christian may be
theirs. If they could gain salvation without effort on their part, they
would be more than happy to receive all that the Lord might give them.
But the Scriptures teach that each individual must cooperate with
the will and power of God. One must "strive to enter in", "put off
the old man", "lay aside every weight," "run with patience", "resist
the devil", and "endure unto the end". Salvation is not of works,
but it must be worked out. It springs from the mediation of Christ
alone, but it is lived out by personal cooperation. While we cannot be
too deeply conscious of our entire dependence on the merits, the
work, and the power of Christ, we must also be aware of our personal
obligation to live daily, by God's grace, a life consistent with the
principles of Heaven. [SDA Commentary]

Many are inquiring, "How am I to make the surrender of myself to
God?" You desire to give yourself to Him, but you are weak in moral
power, in slavery to doubt, and controlled by the habits of your life
of sin. Your promises and resolutions are like ropes of sand. You
cannot control your thoughts, your impulses, your affections. The
knowledge of your broken promises and forfeited pledges weakens your
confidence in your own sincerity, and causes you to feel that God cannot
accept you; but you need not despair. What you need to understand is
the true force of the will. This is the governing power in the
nature of man, the power of decision, or of choice. Everything depends
on the right action of the will. The power of choice God has given
to men; it is theirs to exercise. You cannot change your heart, you
cannot of yourself give to God its affections; but you can choose to
serve Him. You can give Him your will; He will then work in you to
will and to do according to His good pleasure. Thus your whole nature
will be brought under the control of the Spirit of Christ; your
affections will be centered upon Him, your thoughts will be in harmony with
Him.  SC47

The power to will and the power to act must necessarily come
from God, who is the author both of the soul and body, and of all
their powers and energies, but the act of volition and the act of
working come from the man. God gives power to will, man wills through
that power; God gives power to act, and man acts through that power.
Without the power to will, man can will nothing; without the power to
work, man can do nothing. God neither wills for man, nor work's in
man's stead, but he furnishes him with power to do both; he is
therefore accountable to God for these powers.... the power to will and do
comes from GOD; the use of that power belongs to man. (Adam Clarke
Commentary)

The victory is not won without much earnest prayer, without the
humbling of self at every step. Our will is not to be forced into
co-operation with divine agencies, but it must be voluntarily submitted. Were
it possible to force upon you with a hundredfold greater intensity
the influence of the Spirit of God, it would not make you a
Christian, a fit subject for heaven. The stronghold of Satan would not be
broken. The will must be placed on the side of God's will. You are not
able, of yourself, to bring your purposes and desires and inclinations
into submission to the will of God; but if you are "willing to be
made willing," God will accomplish the work for you, even "casting
down imaginations, and every high thing that exalteth itself against
the knowledge of God, and bringing into captivity every thought to
the obedience of Christ." 2 Corinthians 10:5. Then you will "work
out your own salvation with fear and trembling. For it is God which
worketh in you both to will and to do of His good pleasure." MB142,3

Fear and trembling. Paul is not advocating a slavish terror, but
a wholesome self-distrust. The Christian should fear lest his will
not be continually surrendered to Christ, or lest the carnal traits
of character should control the life. He must fear to trust his own
strength, to withdraw his hand from the hand of Christ, or to attempt to
walk the Christian pathway alone. Such fear leads to vigilance
against temptation, to humility of mind, to taking heed lest we fall.
[SDA Commentary]

Fear and trembling. Considering the difficulty of the work, and
the danger of miscarriage. If you do not watch, pray and continually
depend on God, your enemies will surprise you, and your light and life
will become extinct; and then consider what an awful account you must
give to him whose Spirit ye have grieved, and of whose glory ye have
come short. (Adam Clarke Commentary)

It is not the fear and trembling which drives us to hide from
God, but rather the fear and trembling which drives us to seek God,
in the certainty that without his help we cannot effectively face
life. It comes, second, from a horror of grieving God. When we really
love a person, we are not afraid of what he may do to us; we are
afraid of what we may do to him. The Christian's great fear is of
crucifying Christ again. [Barclay Commentary]

The Father in heaven is so interested in His child, and so longs
to have his life in step with His will and His love, that He is
willing to keep the child's guidance entirely in His own hand.  He knows
so well that we do not do what is really holy and heavenly, except
when He works it in us, that He intends His very demands to become
promises of what He will do, in watching over and leading us all day
long.  We may count on Him to teach us His way and show us His path
not only in special trials and hard times, but in everyday
life.....
So simple and delightful can it become to a soul that has
practiced waiting on God, to walk all day in the enjoyment of God's light
and leading.  What is needed to help us find such a life is one
thing: the real knowledge and faith of God as the only source of wisdom
and goodness as always ready and longing to be to us all that we can
possibly need.  Yes, this is the one thing we need.  [Andrew Murray; Time
with God devotional SB]