But why should every minister of the gospel in the New Testament focus on "elementary" doctrines like repentance from sin, faith towards God, baptism, rapture, heaven, hell, etc.? Read Hebrews 5:11-14; 6:1-3

ME: These "elementary" doctrines of the Bible are the foundations on which the weightier doctrines are laid. Any believer who lacks the foundational doctrines, can't grow properly in the faith.

In counting numbers, we do so in this order: 1, 2, 3...

You can't neglect no 1 and attempt to jump to 1,000. You'll certainly crash if you do so.

It's only after believers are grounded in the elementary doctrines that we can take them to higher levels in the doctrines of Christ. Don't be too ambitious to learn deep things of Christ, while you're neglecting the valuable truths of Christ provided for you in shallow waters.