I just checked the table to see that Juventus is on 5th position with 37 points, two points behind Lazio. Since Juventus is a strong club, they will likely overtake Lazio with time, because I don't think that Lazio will be able to maintain the 4th position till the end of the season. Perhaps, the fourth position is open for the clubs on 4th-8th position on the table currently due to little point difference.
To be honest, I don't think Juventus will finish in the top four in Seria A this season. They were busy with their unbeaten league record and even failed to win against a weak club that would have given them more league points. Two points separate Juventus from Lazio, but we're not sure if they'll keep winning after Napoli broke their unbeaten record. Lazio, on the other hand, is capable of maintaining the position until the end of the season, but let's wait to see which team will take over the position at the end.
For me, Juventus still has a big chance to finish in the top four of Serie A this season because the points difference with other teams is not too far. I am sure Thiago Motta will make changes to improve the current situation in order to finish in the top four this season because if Juventus fails to qualify for the Champions League next season, Thiago Motta will most likely be fired.
I quite agree with you with what you said about Juventus finishing on the top four, Lazio's last match really gave Juventus more hope in getting to top four. Still both teams are are not in their best performance. There are only two points in between the two teams, it seems small but difficult to overcome, both teams lost their last match and that didn't sound good, Lazio started this journey well which makes me have confidence in them but along the line they tend to decrease in performance. Since there are still many matches to play maybe they can improve before the season runs out and retain that position.
Currently, the points difference between Lazio and Juventus is just two, which is not much. If Lazio messes up any match now and Juventus wins, Juventus will occupy the fourth position in the Serie A table. However, even for Juventus, there is no assurance that they will finish in the top four because their performances are not stable.
At times, they play better football, but sometimes they just mess up matches. There are matches that Juventus was supposed to win, but they messed up, and that is what has kept them in this position. Right now, Juventus' performance is not that bad they are playing at an average level but I wouldn’t be surprised if they perform worse than this.
I can't say much about Juventus finishing in the top four for now, and the same goes for Lazio. In fact, it’s possible for teams below them to end up in the top four because AC Milan and Fiorentina are very close to Lazio and Juventus, and they still have one outstanding match to play.