INDIANAPOLIS – It began under the sweltering sun of late July and has wound its way into the polar portions of late December.

This 2017 Indianapolis Colts season has run the gamut – from moments of guarded optimism to times where all hope seemed lost.

In so many ways, this has been a season like few we’ve ever seen. It’s been a season in which the biggest story revolved around a player who did not play a single snap (Andrew Luck). It’s been a season in which the team’s very first pass attempt was intercepted and returned for a touchdown. It’s been a season in which attrition has rendered the current roster utterly unrecognizable.

“There’s a lot of this stuff you can’t make up, but it’s the National Football League, so expect the unexpected,” said coach Chuck Pagano, who is widely expected to be dismissed after six seasons.

Yes, 2017 will go down as a season to forget. But it’s also one that can be learned from.

As the Colts enter Sunday’s season finale against the Houston Texans, let’s run down the five biggest lessons to come out of the 2017 season.

>> The value of Andrew Luck

You didn’t need the injury-related absence of Luck in 2017 to tell you he was one of the NFL’s finest quarterbacks. If you witnessed his 40-touchdown season in 2014, his league-record-setting 8,000-plus passing yards in his first two seasons or any of his 18 game-winning drives since 2012, you are well aware of Luck’s contributions.

However, what this season reinforced is that the Colts’ roster, sans Luck, is not very competitive. The extent to which Luck’s play impacts the entire roster was more visible in his absence than when he was present.

Remember all that fourth-quarter magic from Luck? The Colts this season had the exact opposite result, losing six games in which they held halftime leads before ceding those advantages in the second half.

And the offensive production is missing just as Luck himself is missing. The Colts enter Week 17 ranked 31st in total offense (286.9 yards per game). That’s a paltry number for a team that has consistently been among the league’s leaders in yardage. In Luck’s four healthy seasons (he missed nine games in 2015 and all of this year), the Colts have been a top-10 offense three times.

The value of Luck has never been more evident than in a year in which he was not on the field. Perhaps it’s time that changed and this team became less dependent on its sensational but unfairly-burdened franchise quarterback.

>> The defense has potential

There’s a reason General Manager Chris Ballard tackled the defense immediately after his hiring in late January. That is the area of the roster in which there were the biggest voids. It was an old unit. A unit that lacked speed. A unit with a dearth of playmaking.

That’s changed, even if not enough.

We saw Jabaal Sheard and John Simon impact the defense from their outside linebacker spots (even if they were somewhat limited as pass rushers). We saw production against the run from interior linemen Johnathan Hankins and Al Woods. We saw young potential in the secondary, with safety Malik Hooker’s impressive pre-injury playmaking, cornerback Quincy Wilson’s recent emergence and Nate Hairston’s steady play in the slot.

The Colts have some key free agents to tend to, including cornerback Rashaan Melvin. They have to address their lack of edge rush. And they need to beef up their inside linebacker unit.

But this Colts defense in 2017 lost games in which it limited teams to 16, 20, 20 and 13 points. If Luck returns in 2018 and the offense is revived, that’s winning football, folks.

>> Offensive line still unresolved

The Colts’ league-high 55 sacks allowed in 2017 obviously reflects poorly on the offensive line. But the truth is a little more nuanced. Quarterback Jacoby Brissett has brought a lot of that on himself with a lack of decisiveness in his pass attempts. The offensive scheme of Rob Chudzinski, with its long-developing routes and deep quarterback drops, has contributed, too. So, no, the Colts’ line is far from the NFL’s worst.

But it’s not nearly good enough, either. And 2017 has reinforced just how much work is left to be done.

The Colts in the past two NFL drafts have spent five picks on offensive linemen. As it stands, they have little to show for those efforts. Yes, Ryan Kelly, Joe Heag and Denzelle Good have started many games between them, but if this unit still feels unsettled, that’s because it is.

We don’t even know which position is Haeg’s best. We still don’t know if Good is a tease or a legitimate player. We do know that there are better options at left guard than Jeremy Vujnovich.

Look for Ballard to consider free agency as an option for upgrading his offensive line. Given the slow development of rookie offensive linemen these days – i.e. Le’Raven Clark – if you want faster results, it’s likely going to cost you.

The Colts know this. And, after 2017, they might be willing to come to terms with it. The key will be getting the right players. Remember, former GM Ryan Grigson spent considerable money on the offensive line in free agency, too.

>> The 2017 class has potential

The current rookie class will probably never rival that amazing 2012 assemblage of players the Colts selected. Andrew Luck, T.Y. Hilton, Dwayne Allen and Coby Fleener are probably going to trump most anything else.

But the Colts’ 2017 rookies look like they will be impactful in their own ways. First-round pick Hooker has fabulous potential and was everything the Colts hoped he’d be until he was injured in Week 7.

Wilson, the team’s second-round choice, was hampered by a knee injury much of the season. Then, coaches stubbornly were slow to integrate him into the lineup. But now that he’s been a regular in recent weeks, we can see his physical, man-to-man skill set. At just 21, he has limitless potential.

The production hasn’t been there for third-round pick Tarell Basham (two sacks), but he’s shown more of a presence in the latter stages of the season, perhaps setting the stage for a bigger jump in 2018. The evaluations from coaches have grown progressively more positive as the season has worn on. There’s still tons of untapped potential there.

Fourth-round pick Marlon Mack has a bit of an identity crisis that isn’t all his fault. Is he a situational back? A change-of-pace back? Can he be an every-down runner?

The presence of Frank Gore and some of the odd usage of Mack have perhaps limited his impact, but Mack has done a good job of consistently making big plays. If nothing else, he put defenses on notice in 2017 and they now know he has game-breaking potential each time he touches the football. If Mack can stay healthy through the coming offseason – he missed too many practices last summer – he will grow as a pass protector and hopefully make some gains in this vital part of his game.

Fourth-round choice Grover Stewart, fifth-round pick Hairston and fifth-rounder Anthony Walker all have managed to have an impact in 2017. That’s more than you can often expect from later-round picks. This is especially true of Hairston, who was the starting nickel corner all season.

The jury is still out on Ballard, but his first draft class has been very impressive and will provide building blocks for the Colts in the coming years. It’s a great first entry on the resume of the first-year GM.

>> The AFC South is for real

When the Colts emerge from this downward spiral they’ve been on and try to again become a factor in the division race, they’ll find a very different AFC South. The Jacksonville Jaguars are clearly not a flash in the pan. Teams built on defense rarely are. The Titans still have flaws, but they are one victory away from clinching a playoff berth as the division’s second postseason team this year.

Houston is currently in disarray given their debilitating injuries, but the flashes we saw from rookie quarterback Deshaun Watson should capture the Colts’ undivided attention. If Watson returns from his knee injury in the same form, the complexion of the division changes even more.

Remember when the Colts won 16 consecutive games in the division without breaking a sweat? Those days appear to be over. The 2017 season has made it clear it’s a new day in the AFC South. And the Colts are going to have to prove they can keep pace.

Lesson learned.

Follow Colts Insider Stephen Holder on Twitter: @HolderStephen.