Predestination and election are "decrees."
Predestination and Foreknowledge: Are People Predestined to Heaven and Hell?
I am glad you are convinced of Total Depravity. The Scripture states that we are dead in trespasses and sin (Eph. 2:1-3). Mind us before Christ, we are blind, and cannot see the truth; we are deaf and cannot hear the calling of God; we are dumb and cannot speak forth the truth of God from the heart; we have withered hands and cannot reach out for the things of God; we are lame and do not walk in the Spirit; and since we are dead and continually decompsing, we really stink of sin.
Before Christ we have total inability to do anything righteous for the glory of God, etc. Paul writing on total inability says, "For the mind that is set on the flesh is hostile to God, for it does not submit to God's law; indeed, it cannot" (Rom. 8:7). Note our condition before Christ. We are: (1) hostile to God, (2) do not submit to God's law, and (3) cannot submit to the law of God. So, before Christ we are in a rut; we cannot deliver ourselves from sin.
However, the news gets even worse. God, as his law, is holy, just, and good (Rom. 7:12). Briefly stated, since God is holy he cannot condone sin in in his presence without judging it. He is angry with the wicked every day (Psa. 7:11). While he is patient (Rom.2:4), ultimately he must necessarily according to his divine nature judge sin and the sinner, fully. He will not continue to look at evil and wrong and traitors and remain silent (Hab. 1:13). He will execute his judgment upon all the earth.
So, we are in a straight betwixt two; we cannot deliver ourselves and God according to his divine nature cannot deliver us, as he must judge sinners. But ....
Enter predestination/election. Before our sin (Eph. 1:4), God elected us to his grace, mercy and to be his people, etc. Before our sin, God predestined Christ to go to the Cross to die in our place (1 Pet. 1:18-20: Acts 2:23-24: 4:27-28). God's holy and just wrath against his elect's sin was fully poured out upon his only begotten and sinless Son, Jesus Christ. God's wrath has been appeased for his elect (1 John 2:1; 4:10) and only his elect. Christ healed his people and now they see, hear, speak, reach out, and walk in the things God (albeit not perfectly,1 John 1:9; but they (1) are not hostile towards God; as they are his children, (2) they desire to fully and completely submit to God's law, and (3) can submit to God's law - see Rom. 8:7 and in glory they will do it perfectly, et. al.), as this is what they have been saved unto (Eph. 2:10; Tit. 2:14); to bring glory to the one who saved them. Since, we are no longer dead, but born again from the dead (1 Pet. 1:3), we no longer stink, but "... are the aroma of Christ to God among those who are being saved and among those who are perishing" (2 Cor. 2:15).
So, without Predestination there would be no salvation possible.
In addition, not only is the doctrine of P necessary for intial saving faith, it also assists in us in daily living. As others have said, God is sovereign in what happens - everything that happens - was/is "ordained" by him. A person understanding this will react differently to situations than a person who thinks otherwise concerning providence, etc. Knowing that God is sovereign, Joseph reacted differently towards his own brothers (Gen. 50:20). Some people when they do not understand predestination, providence, etc. will literally get mad at God when stuff happens - and stuff will happen to be sure. However, with a proper view of God being in control concerning everything - from the number of hairs on your head to the even the events of 9-11 - allows one not to get angry at God, but to realize that he is still and always will work things together for their good, et. al. You will become a more patient person, less "reactive" in sin (less fleshly responses) and more "active" in righteousness, etc. Peter's best friend was murdered on the Cross. Peter had emotions just like we do. How would you react towards the people that murdered your spouse, child, etc? What did Peter do? He preached a sermon on the sovereignty of God in the death of of his best friend (Acts 2:23-24).
Here is an example of how providence, etc. effected even the lineage of Christ:
Does God Change His Mind?
The doctrine of predestination and providence impact every area of life and every other biblical doctrine. In essence it helps one make sense of life. Making sense of it all is a major part of living it pure before God.
It is a doctrine that very few understand as much as they should and most churches fall especially short in making the doctrine clear, et. al.
Have a blessed weekend.