Learned the secret (one word in Greek) (3453) (mueo = root word for mustes meaning "one initiated" which in turn is the source of "mystery" or musterion) means to be initiated. It was used by the pagan religions with reference to their “inner secrets.” Paul is saying in essence “I have been initiated, I possess the secret”. Mueo was the common term used to describe the initiation rites required of anyone seeking to enter into the secrets of the ancient mystery religions. Mueo means to learn the secret of something through personal experience or as the result of initiation. In those mysteries, it was only the “initiated” who were made acquainted with the lessons that were taught there. Paul’s initiation was not a secret affair for he learned from the hard experiences in life. Eadie adds that mueo is borrowed from the nomenclature of the Grecian mysteries, and signifies the learning of something with preparatory toil and discipline...There is no idea of secret training. (The Epistle to the Philippians) Paul says that he had been initiated into the lessons taught by trials and by prosperity. The secret and important lessons which these schools of adversity are most suited to teach, Paul had had ample opportunity to learn from and he had faithfully embraced the doctrines he had been taught. Are trials your teachers or your tormentors? Let us not miss the opportunities God provides us to grow in grace and in understanding of the sweet "secret of contentment". Once again Paul borrows from the vocabulary of his pagan environment just the right word that would be readily understood by his readers and which expresses accurately the idea he wished to impart. Paul is not saying that he automatically or instantaneously entered into the secret of a contented life, but that he came to know this secret through a process that would be analogous to the rites of an initiation. Paul was saying that he had been "initiated" through disciplining circumstances into the "mystery" of Christ in Him the hope of Glory. When he was born again he was possessed all of Jesus he would ever possess but it was through the variegated trials and circumstances of his subsequent life that the Spirit taught him that Christ was his very life and his continual source of power and contentment. Spurgeon commenting on how Paul learned the secret says... You may now ask by what course of study did he acquire this peaceful frame of mind? And of one thing we may be quite certain, it was by no stoic process of self-government, but simply and exclusively by faith in the Son of God. You may easily imagine a nobleman whose home is the abode of luxury, traveling through foreign parts for purposes of scientific discovery, or going forth to command some military expedition in the service of his country. In either case he may be well content with his fare, and feel that there is nothing to repine at. And why? Because he had no right to expect anything better; not because it bore any comparison with his rank, his fortune, or his social position at home. So our apostle. He had said "Our conversation or citizenship is in heaven." (see note Philippians 3:20) Traveling through earth as a pilgrim and stranger he was content to take travellers fare. Or entering the battle field, he had no ground of complaint that perils and distresses should sometimes encircle his path, while at other times a truce gave him some peaceful and pleasing intervals (Contentment) Vine adds that learned the secret is in the passive voice, (which speaks of action exerted on one from without or from an outside force, in this case of course the Spirit of God taking Paul from glory to glory) “I have been initiated,” and the perfect tense (past completed action with present ongoing result or effect) conveys the thought of the abiding effects of the initiation. Paul’s use of this word indicates that this constant and complete contentment, whilst possible to all believers, involves many and varied testings, costing self-denial, demanding fervent prayer and abstention from many a thing which might be considered not only legitimate but consistent with improved circumstances. Such contentment brings present peace and future reward." The effort called for to learn the secret reminds one of Paul's instruction to Timothy to "have nothing to do with worldly fables fit only for old women. On the other hand, discipline (gymnazo -command to make this a habit of your life, literally to train in the gym stripped of all clothes which would encumber one's training!) yourself for the purpose of godliness (train yourself, keeping yourself spiritually fit) for bodily discipline is only of little profit, but godliness (spiritual training) is profitable for all things (in everything and in every way), since it holds promise for the present life (life that now is, literally "the now life") and also for the life to come ("of the coming future life"). (see notes 1Timothy 4:7; 1Timothy 4:8) (Vine, W. Collected writings of W. E. Vine. Nashville: Thomas Nelson ) Clarke notes that Paul is saying I have passed through all these states; I know how to conduct myself in each, and how to extract good from all. And he had passed through these things, especially the hardships, so that he had learned the lesson perfectly, as the word memuemai (initiate) implies; he was thoroughly instructed; fully initiated into all the mysteries of poverty and want, and of the supporting hand of God in the whole. See here the state to which God permitted his chief apostle to be reduced! And see how powerfully the grace of Christ supported him under the whole! How few of those who are called Christian ministers or Christian men have learned this important lesson! When want or affliction comes, their complaints are loud and frequent; and they are soon at the end of their patience.