What the context of Acts 2 is really about

The Context on the Day of Pentecost was: Speaking in tongues to multiple nations. The focus has nothing to do with the phrase "as the Spirit gave them utterance." 

To place a weighty meaning upon these words, such as I prayed for a person to receive the Baptism in the Holy Spirit, but the Holy Spirit provided no initial evidence of tongue-speaking; therefore, the Spirit didn't give utterance, but may do so tomorrow, ignores the both context and purpose of Acts 2.

What the apostles needed, at this point in their history, was not moral courage or devoutness of spirit; for they had already recovered from the alarm produced by the crucifixion and were now boldly entering the temple together every day and spending their whole time in devout worship. 

Their defects were such that no degree of courage or of piety could supply. It was power that they wanted—power to remember all that Jesus had taught them; to understand the whole meaning of all his words; of his death; of his resurrection; to pierce the heavens, and declare with certainty things which had transpired there; and to know the whole truth concerning the will of God and the duty of men. 

There is only one source from which this power could be derived, and this the Saviour had promised them, when he said, “You shall receive power (dunamin) when the Holy Spirit comes upon you.” 

• But power to establish the kingdom and to proselyte the world involved not merely the possession of the miraculous mental power above named, but the ability to prove that they did not possess it. This could best be done by an indisputable exercise of it. 
• To exercise it, however, by merely beginning to speak the truth infallibly, would not answer the purpose, for men would inquire.
• How can you assure us that what you say is the truth? To answer this question satisfactorily, they gave such an exhibition of the superhuman knowledge which they possessed as could be tested by their hearers. 
• They might have done this by penetrating the minds of the auditors and revealing their secret thoughts or past history to them, but this would have addressed only one individual at a time. 
• Or they might, like the prophets of old, have foretold some future event, the occurrence of which would prove their inspiration; but this would have required some considerable lapse of time, and would not, therefore, have answered the purpose of immediate conviction. 

There is, indeed, but one method conceivable by which they could exhibit this power to the immediate conviction of a multitude, and that is the method adopted on this occasion, speaking in other tongues, as the Spirit gave them utterance. 

If anyone doubts this, let them imagine and state, if they can, some other method. True, they might have wrought miracles of healing, but this would have been no exhibition of miraculous mental endowments. 

The proof, in this case, is direct, being an exhibition of the power which they claimed. By the only method, then, of which we can conceive, the apostles, as soon as they became possessed of the promised power, exhibited to the multitude an indisputable exercise of it.

It should be noted that this exhibition could only serve its purpose when individuals were present who understood the languages spoken. Otherwise, they would have no means of testing the reality of the miracle.