Please accept my humble obeisance. All glories to Srila Prabhupada
Austerity is Training the BODY to live in certain Terms & Conditions generally a very regulated & disciplined life.
Austerity & Penance some many say it is relative term.
To one who lives in AC 24/7 living without it is Austerity
To one who lives without AC living in extreme climates is Austerity
To one who eats 6 times a day when asked to eat only three times is Austerity for them.
To one who eats only one time a day is asked to fast for a week only on water is Asterity for them
To one who is not used to following 4 Regulative Principles is Austerity for Him if He has to follow
Coming to penance
Penance is Training the MIND to live in certain Terms & Conditions generally a very regulated & disciplined life.
To a Karma Yogi - Vanaprasta or Sanyas Life is Penance
To a Jana Yogi - to liberate oneself is penance
To a Hata Yogi Practicing Hata Yoga by controlling the life air and transporting oneself to the desired destination is penance
To a Bhakti Yogi Engaging Devotees full energies in Devotional Service through cooperation is penance.
Those who undergo severe austerities & penances not recommended in the scriptures, performing them out of pride and egoism, who are impelled by lust and attachment, who are foolish and who torture the material elements of the body as well as the Supersoul dwelling within, are to be known as demons. BG 17.5-6
Leading a austere life and doing penance means leaving your comfort zone and entering into your challenge zone. That is called progress. In a ladder which ever step we are on, the moment we start feeling comfortable we need to move up.
There is striking example if we all would have observed which devotees can relate to. Those who have traveled to Trupati and climbed Tirumala hill via walk/climbing the steps at palaces we take rest when very tired with body & mind. Sometimes we are tired by body but the mind pushes us to go forward by sending signals to take rest. The mind has decided to climb and the body becomes an instrument for the mind to achieve its desires. And when the body shows sign of tiredness the mind signal for rest. This is how we progress, some devotees at a stage take rest in a given level and others surpass them due to having a fit body for the mind to execute its plan. So there is coordination between mind and body.
This one above example can give rise to many examples form even material angle if ones who wants to understand..
Therefore the word progress appears to be a relative term. From the below BG 6.47 Commentary by Madhavachary he shows a progress path to each soul, who is situated comfortable and guides Him to adopt a progressive path that takes a sould higher and higher on the spiritual ladder.
The Garuda Purans states that: In comparison to all yogis and aspirants, meditation on Lord Krishna or His Vedically authorised incarnations is 100,000 times superior to meditation on others. In the Narada Purana it states: Meditation with knowledge of the Supreme Lord Krishna is infinitely superior to meditation without knowledge of the Supreme Lord Krishna. Better than even meditation with knowledge of the Supreme Lord Krishna is direct perception of the Supreme Lord Krishna. Better than even direct perception of the Supreme Lord Krishna is communion with devotion to the Supreme Lord Krishna.
Superior to austerities and penance is meditation
Now begins the summation.
Superior to austerities and penance is meditation. Better than meditation without realisation is meditation with realisation. For those who meditate with realisation that are not devotees of Lord Krishna or His Vedically authorised incarnations, whatever they meditate on has no efficacy. The persons who see similarity between other gods and the Supreme Lord Krishna, the persons who do not see Lord Krishna as superior to all other gods, the persons who believe other gods to be more elevated than the Supreme Lord Krishna, those person who are indifferent to the Supreme Lord Krishna and those persons who are irreverent and spiteful to the Supreme Lord Krishna are all classified as non-devotees. Among the devotees who do not possess the offensive mentality previously elucidated. Those special devotees who worship the Supreme Lord Krishna exclusively with love and devotion are the most elevated of all. Sri Dattatreya a lila avatar or incarnation of the Supreme Lord Krishna states: The Supreme Lord is installed directly in the center of a Vaisnava or Brahmana family as the leading member and is thus lovingly and devotedly worshiped as such.
Krsna in BG 12.8-12 gives us the progress path based on our ability and as we take rest when tired He gives some leverages to those who have problems with fitness.
BG 12.8: Just fix your mind upon Me, the Supreme Personality of Godhead, and engage all your intelligence in Me. Thus you will live in Me always, without a doubt.
BG 12.9: My dear Arjuna, O winner of wealth, if you cannot fix your mind upon Me without deviation, then follow the regulative principles of bhakti-yoga. In this way develop a desire to attain Me.
BG 12.10: If you cannot practice the regulations of bhakti-yoga, then just try to work for Me, because by working for Me you will come to the perfect stage.
BG 12.11: If, however, you are unable to work in this consciousness of Me, then try to act giving up all results of your work and try to be self-situated.
BG 12.12: If you cannot take to this practice, then engage yourself in the cultivation of knowledge. Better than knowledge, however, is meditation, and better than meditation is renunciation of the fruits of action, for by such renunciation one can attain peace of mind.