In chapter 4 of the Book of Amos, verses 1-3 are talking about people who pervert the truths of the church. They will fall into falsities in outermost things.

In the Bible, fish represent "lower" things than mammals, so we can interpret the fishhooks in verse 2 as meaning being caught and held fast in natural or lower things.

Verses 4-6 are about acts of worship such as tithes and sacrifices. These look similar to genuine worship, but are only external sorts of things. We can tell because ‘teeth’ (in verse 6) represent ultimates or outermost things (see Secrets of Heaven 6380). It follows that “cleanness of teeth” would mean outermost things that look good but only imitate genuine worship. The Lord exhorts, “Yet you have not returned to me.”

Verses 7-8. Some things true will remain, when where there are too many false ideas, the truths don't get through. This can be seen where the Lord says, “I made it rain on one city; I withheld rain from another city... where it did not rain the part withered.” Again the Lord exhorts, “Yet you have not returned to me.”

Verse 9. Afterward all things of the church are falsified, shown by blight attacking the gardens, vineyards, fig tree and olive trees. The last three represent spiritual, natural and celestial things, or all the things of spiritual life. “Yet you have not returned to me,” says the Lord.

Verses 10-11. The Lord explains the devastating things he allowed to happen: plague in Egypt, death of young men by swords, stench in the camps, Sodom and Gomorrah. This is because they are profaned by sensual knowledges. Profanation means the mixing of good and evil together. (See Secrets of Heaven 1001[2]).

This extends to all things of the church, with the church being the Lord’s kingdom on earth (Secrets of Heaven 768[3]).

With profanation “as soon as any idea of what is holy arises, the idea of what is profane joins immediately to it,” (Secrets of Heaven 301).

Now there is hardly anything left. “Yet you have not returned to Me,” says the Lord again.

Verses 12-13: Because people adamantly remain in their profane ways, they are warned, “Prepare to meet your God!”. This is the God powerful and mighty, “who forms mountains, and creates the wind,” and even more close to home, “Who declares to man what his thought is.” As intimately a knowing as that is, the Lord’s love for all humanity is contained in His exhortations for them to turn themselves to Him.

See, for example, Luke 6:44-45, and True Christian Religion 373.

352. 'The firstborn of the flock' means the holy which is the Lord's alone. This becomes clear from the firstborn in the representative Church, where everything was holy because it had regard to the Lord, who alone is 'the Firstborn'. Love and faith deriving from it are the firstborn. All love is the Lord's and not a trace of it man's, and this is why the Lord alone is 'the Firstborn'. This was represented in the Churches of the ancient era by the requirement to consecrate the firstborn of man and of beast to Jehovah, Exodus 13:2, 12, 15. It was also represented by the tribe of Levi, which in the internal sense means love - though Levi was born later than Reuben and Simeon, who in the internal sense mean faith - being taken instead of all the firstborn and becoming the priesthood, Numbers 3:40-46; 8:14-20. That the Lord as regards His Human Essence is the Firstborn of all is clear from the following statement in David,

He will cry to Me, You are My Father, My God, and the Rock of My Salvation; I will also make Him as the Firstborn, supreme over the kings of the earth. Psalms 89:26-27.

And in John,

Jesus Christ, the Firstborn from the dead, and Prince of the kings of the earth. Revelation 1:5.

Please note that the firstborn of worship mean the Lord, while the firstborn of the Church mean faith.