Why say AMEN at the end of a song?
Who knows? There is little need for it though it is not unscriptural for a brother to do so. The word ‘amen’ means so let it be. Sometimes after a song that is especially heart-stirring you may hear someone say amen, like during good hard preaching when someone feels the preacher “hit the nail on the head.” As well, properly at the end of a well understood, scriptural prayer the brethren can and should say “amen.” By the way, the particular songs sung by the church should be scriptural because we are teaching through that song and we could NOT say amen to anything that would mislead or cause someone to sin, be it a song, sermon, or prayer. (Read these scriptures: I Cor 1:20; Rev 3:14; I Cor 14:15-17; Col 3:16-17; Eph 5:19)
If Heaven has a size, does Hell?
Yeah, it’s BIG! Let me first say that there are a couple of usages of hell. One means the grave or place of the unrighteous dead before the final judgment. This word is ‘Sheol’ in the Hebrew and ‘Hades’ in the Greek. The place of those who are forbidden to enter heaven after the great judgment is called, ‘Tartarus’ in Hebrew and ‘Gehenna’ in Greek. All of these words are translated in English as hell. In particular you are asking about Gehenna, or the “lake of fire.”
Though no literal dimension is given, it’s deep enough to immerse (baptize) ALL the wicked into utter oblivion so that they are never a disturbance to God again. However, in hell souls will not die like one dies on the earth. No, this will be an eternal ongoing agony where the peace of death will never come! (Read these scriptures: Mark 9:42-48; Rev 20:10-15; Matt 10:28; James 3:6; II Peter 2 [whole chapter]; Isaiah 5:14; Matt 3:1-11; Matt 20:20-23.)
How could the Angels even know to disobey? How could they be jealous?
The HOW is somewhat of a mystery to us. The WHY is easy to figure. Man was the crowning step in the creation. Satan did not like sharing this glory with mankind. He pulled many other angels with his persuasion to rebel against God in an effort to destroy man’s relationship to the Creator. (Read these scriptures: II Peter 2:1-11; Matt 25:41; I Tim 4:1-7; I John 3:8-10; Job 1:6-12; Psalm 8; I Cor 11:9-10; I Peter 1:12; Jude 1:6; Rev 12:7-11.)
Will we know each other in Heaven? Will we have equal understanding?
Yes and yes. Jesus is our perfect example of what happens after we die. Jesus died, was buried, rose again a short while later, was seen and recognized of His friends, had flesh and bone, was able to eat food, was NOT a ghost, ascended into heaven. We will do likewise. Death occurs when the spirit leaves the body. the spirit goes away for a while to the place of the dead (righteous in Paradise and the unrighteous in Hades). At the resurrection everyone will be raised up with a glorified body perfect for eternity (this is the time when the spirit comes back to the body, only the body will be better than the earth-made one). The righteous will ascend into heaven after judgment, while the unrighteous shall be cast away for all eternity into everlasting torture. We will be recognizable just as Jesus was. We will have a new improved body that will look like the old familiar one we had on earth. Children and infants will perhaps have some level of maturity to their appearance as the elderly may have youth.
We will have an understanding in heaven because all things will be revealed to us as children of God and brothers and sisters to Christ. (Read these scriptures: Matt 28:9-10; Mark 16:9-14; Luke 24:13-53; Acts 1:2-11; Like 16:19-31; I Cor 15:16-28; I Cor 13:12; I Thess 4:13-18; James 2:26; Heb 9:27; I Cor 1:1-8; I Peter 1:6-16; Rom 8:18; I Peter 4:13; I Peter 5:1; I John 3:2)