But why should I tremble, since God is taking care of the work?
Sorry if I don't sound too bright here. I do know there is nothing I can do to add to my salvation, that's why this verse is difficult for me, I guess.
There are numerous good reasons to tremble at the presence of almighty God.
Ecc 12:13 Let us hear the conclusion of the whole matter: Fear God, and keep his commandments: for this is the whole duty of man.
The book of Ecclesiastics should give you ample material to understand why we ought to, like Paul, be in fear and trembling.
2Co 7:15 And his inward affection is more abundant toward you, whilst he remembereth the obedience of you all, how with fear and trembling ye received him.
Eph 6:5 Servants, be obedient to them that are your masters according to the flesh, with fear and trembling, in singleness of your heart, as unto Christ;
The fact is, when Jesus comes back, he's judging the living AND the dead, and our works will be put to the test in fire.
Consider what Jesus said here, about "stripes"
Luk 12:43 Blessed is that servant, whom his lord when he cometh shall find so doing.
Luk 12:44 Of a truth I say unto you, that he will make him ruler over all that he hath.
Luk 12:45 But and if that servant say in his heart, My lord delayeth his coming; and shall begin to beat the menservants and maidens, and to eat and drink, and to be drunken;
Luk 12:46 The lord of that servant will come in a day when he looketh not for him, and at an hour when he is not aware, and will cut him in sunder, and will appoint him his portion with the unbelievers.
Luk 12:47 And that servant, which knew his lord's will, and prepared not himself, neither did according to his will, shall be beaten with many stripes.
Luk 12:48 But he that knew not, and did commit things worthy of stripes, shall be beaten with few stripes. For unto whomsoever much is given, of him shall be much required: and to whom men have committed much, of him they will ask the more.
Luk 12:49 I am come to send fire on the earth; and what will I, if it be already kindled?
Luk 12:50 But I have a baptism to be baptized with; and how am I straitened till it be accomplished!
Luk 12:51 Suppose ye that I am come to give peace on earth? I tell you, Nay; but rather division:
Obviously, the part about receiving stripes is "part of" the gospel, the words of the Father delivered by the Son of God Jesus. Thus, those who think there will be no stripes are believing a lie. There will be stripes, and more for those who knew and did not