Our Advocates and Adversary
The English word advocate originated from a Latin word meaning to speak (i.e. the vocal in advocate). God's people have advocates (Christ and the Holy Spirit - see below) to present our "case" before God (see also What Is Jesus Christ Doing Right Now?), but during the time of greatest tribulation (see Trials and Tribulations), God Himself will be the Advocate for His people:
"10:19 But when they deliver you up, take no thought how or what ye shall speak: for it shall be given you in that same hour what ye shall speak. 10:20 For it is not ye that speak, but the Spirit of your Father which speaketh in you." (Matthew 10:19-20 KJV)
On the other hand, the English word adversary originated from a Latin word meaning to oppose (the "verse" means to turn). Satan too is a speaker; he corrupted the first humans with words and has been doing the same, with a purpose, ever since i.e. Satan wants to re-verse those who con-vert, to turn back to Satan those who have turned to God - a far worse condition, after one knows better, than when one is merely blindly misled.
"2:20 For if after they have escaped the pollutions of the world through the knowledge of the Lord and Saviour Jesus Christ, they are again entangled therein, and overcome, the latter end is worse with them than the beginning. 2:21 For it had been better for them not to have known the way of righteousness, than, after they have known it, to turn from the holy commandment delivered unto them. 2:22 But it is happened unto them according to the true proverb, The dog is turned to his own vomit again; and the sow that was washed to her wallowing in the mire." (2 Peter 2:18-22 KJV)
"After that ye have suffered a while, make you perfect, stablish, strengthen, settle you"
The Greek word (pronounced) par-ak-lay-tos is found only in the writings of the apostle John, first in the Gospel book of John, where Jesus Christ uses the word in reference to the Holy Spirit, and in John's first epistle in which it refers to Christ Himself. Although the same Greek word was originally written in both, the King James translates it as "Advocate" for Christ and "Comforter" for the Holy Spirit.
Christ's instructions about the "Comforter":
"14:15 If ye love me, keep my commandments [see The Two Great Commandments and The Ten Commandments]. 14:16 And I will pray the Father, and he shall give you another Comforter, that he may abide with you for ever; 14:17 Even the Spirit of truth; whom the world cannot receive, because it seeth him not, neither knoweth him: but ye know him; for he dwelleth with you, and shall be in you. 14:18 I will not leave you comfortless: I will come to you. 14:19 Yet a little while, and the world seeth me no more; but ye see me: because I live, ye shall live also. 14:20 At that day ye shall know that I am in my Father, and ye in me, and I in you. 14:21 He that hath my commandments, and keepeth them, he it is that loveth me: and he that loveth me shall be loved of my Father, and I will love him, and will manifest myself to him." (John 14:15-21 KJV)
Later, John's use of the word to refer to Christ (note, in both cases, that keeping His Commandments on our part is vital to the Comforter and the Advocate being there, doing their part):
"2:1 My little children, these things write I unto you, that ye sin not. And if any man sin, we have an advocate with the Father, Jesus Christ the righteous: 2:2 And he is the propitiation for our sins [see Christ's Mercy Seat]: and not for ours only, but also for the sins of the whole world.
The adversary on the other hand hates God's Commandments - and everyone who strives to obey them:
"12:17 And the dragon [see Dragons] was wroth with the woman, and went to make war with the remnant of her seed, which keep the commandments of God, and have the testimony of Jesus Christ." (Revelation 12:17 KJV)
Satan is the adversary of anything and anyone that has good - an adversity that, despite Satan's evil, has good for those who steadfastly resist the devil (see the Fact Finder question below).
"5:6 Humble yourselves therefore under the mighty hand of God, that he may exalt you in due time: 5:7 Casting all your care upon him; for he careth for you.
Fact Finder: How is Satan's resistance like a dumbell to a weightlifter? Does his opposition make Christ's people stronger than they would be if they faced no challenges?